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OK    TIIK 


BOSTON  SOCIETY  OF  NATUML  IlKTOllY 


VOLUME  r,,  NUMBER  0. 


THE  ANATOMY  AND  DKVI]f,OPMFNT  OT  ^ASSIOPEA  XAMACHANA. 


liv   ;i.)J.LjIT   I'AYNK   HlGKi.OW. 


BOSTON: 


BY   T'.?.   socin'ry. 


usT,   1900. 


EXCHANGE 


^It-Cr 


BIOLOGY 

UbRARY 

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BIOLOGY 

LIBRARY 

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6.     THE  ANATOMY  AND  DEVELOPMENT  OF  CASSIOPEA 
BY  ROBEKT  PAYNE  BIGELOW. 

INTRODUCTION. 

During  the  summer  of  1891  the  Marine  Laboratory  of  the  Johns  Hopkins  University 
was  stationed  in  the  Island  of  Jamaica.  It  was  at  Port  Henderson,  —  a  little  hamlet 
situated  at  the  west  side  of  the  mouth  of  Kingston  Harbor,  at  the  point  where  the  Salt 
Pond  Hill,  eight  hundred  feet  high,  descends  to  the  salinas  and  mangrove  swamps 
surrounding  the  mouth  of  the  Rio  Cobre.  On  the  other  side  of  the  hill,  and  to  the  south 
of  it,  there  is  a  considerable  body  of  salt  water,  known  as  the  Great  Salt  Pond.  It  is 
completely  .separated  from  the  sea,  but  only  by  a  beach  of  sand,  which  at  its  narrowest 
part  is  not  more  than  a  few  rods  in  width;  and  it  is  said  by  those  who  live  near  that  in 
times  of  storm  or  freshet  this  barrier  may  be  broken  through. 

One  morning  in  June  Dr.  G.  W.  Field  was  hunting  birds  along  the  seaward  shore  of 
this  pond,  and  came  upon  a  little  bay  that  forms  a  deep  indentation  in  the  barrier  and  is 
connected  with  the  pond  by  a  narrow  inlet.  The  bay  is  overhung  by  low  cashaw  and 
mangrove  trees.  At  one  side  is  a  sunny  sandy  spot  where  a  crocodile  had  made  its  bed, 
and  a  fresh  zigzag  mark  showed  where  it  had  recently  slid  into  the  water.  A  school  of 
fish  was  circling  about  in  the  clear  water,  and  barnacles  and  sea-anemones  spread  their 
tentacles  from  the  submerged  roots  of  the  mangroves,  while  the  bottom  at  the  inner  end 
of  the  bay  was  completely  carpeted  by  a  colony  of  beautiful  rhizostomatous  medusae. 

A  few  very  small  specimens  might  be  seen  swimming  about,  but  most  of  the  medusae, 
especially  the  larger  ones,  would  not  ordinarily  leave  the  bottom.  They  lay  there  upon 
their  backs,  with  their  voluminous,  branching  mouth  parts  spread  out  over  their  discs, 
which  were  motionless,  except  for  occasional  flaps  of  their  margins.  If  any  of  these 
animals  were  disturbed,  they  would,  however,  swim  about  like  ordinary  medusae ;  but 
before  long  they  would  settle  down  again  and  assume  their  usual  attitude  upon  the  bottom. 

1  An  earlier  draft  of  this  paper  was  accepted  in  May,  1892,  by  the  Board  of  University  Studies  in  the  Johns  Hopkins 
University  as  a  thesis  for  the  Degree  of  Doctor  of  Philosophy.  During  the  years  1891-92  and  1892-93  I  held  the  Adam  T. 
Bruce  Fellowship  in  the  Johns  Hopkins  University,  and  was  thus  enabled  to  make  a  second  journey  to  Jamaica.  Publication 
has  been  delayed  in  order  that  the  results  of  this  journey  might  be  incorporated  in  the  paper,  and  it  is  hoped  that  the  greater 
accuracy  and  completeness  thus  obtained  have  added  materially  to  its  value. 


.1.9.2  -    •    •••.  ROBERT   PAYNE   BIGELOW   ON 


Within  this  limited  area  there  were  countless  numbers  of  them,  and  in  many  places  they 
were  so  thickly  spread  that  their  margins  touched  upon  all  sides,  or  even  overlapped. 

The  spectacle  presented  by  this  collection  of  medusae  was  truly  marvelous ;  and  in 
order  to  show  something  of  it  to  the  rest  of  us,  Dr.  Field  gathered  a  pailful  of  specimens 
and  brought  them  to  the  laboratory.  Upon  examination  they  were  all  found  to  belong  to 
a  single  new  species  of  Cassiopea,  —  a  genus  of  which  only  one  species  was  known  to 
occur  outside  of  the  Red  Sea,  Indian  Ocean,  and  southwest  Pacific  ; l  and  this  pailful, 
taken  up  at  random,  contained  both  adults  and  young  in  various  stages  of  growth. 

Professor  Brooks  made  drawings  of  some  of  these,  and  then  I  made  a  visit  to  the 
Salt  Pond  to  obtain  more  of  the  young  medusae,  and  at  the  same  time  I  collected  sub- 
merged bits  of  wood  and  stems  of  plants.  My  hopes  were  more  than  realized  when,  upon 
examining  these  objects  in  the  laboratory,  I  found  them  thickly  studded  in  places  with 
scyphistomas  in  various  stages  of  development.  I  was  particularly  delighted  when  I 
noticed  in  one  of  the  largest  larvae  certain  glistening  spots  in  the  bases  of  the  tentacles 
and  found,  on  putting  them  under  the  microscope,  that  they  were  unmistakably  masses  of 
calcareous  bodies  that  would  form  part  of  the  marginal  sense  organs  of  the  adult.  They 
excited  my  interest,  especially  as  I  had  been  studying  the  development  of  these  structures 
in  Discomedusae  ('90) ,  and  had  been  unable  hitherto  to  obtain  the  early  stages. 

After  this  discovery  I  began,  with  the  advice  of  Professor  Brooks,  to  make  a  careful 
study  of  this  species,  with  the  intention  of  carrying  the  investigation  of  its  anatomy  and 
development  as  far  as  the  limited  amount  of  time  at  my  command  would  allow.  Prelim- 
inary accounts  of  my  results  were  published  in  1892  (Bigelow,  '92,  a,  b  and  o) .  In  the 
spring  of  1893  I  had  another  opportunity  to  visit  Port  Henderson  with  a  party  from  the 
Johns  Hopkins  University,  and  was  able  to  make  important  additions  to  my  earlier 
observations. 

During  the  first  visit  to  Jamaica  I  was  unable  to  find  Cassiopea  outside  of  the  one 
locality  that  I  have  described,  and,  although  both  the  adults  and  the  young  in  nearly  all 
stages  were  present  at  this  place  in  such  great  numbers,  searches  for  males  and  for  females 
with  ripe  eggs  were  equally  fruitless.  The  great  abundance  of  young  and  the  range  in 
their  apparent  ages  was,  therefore,  surprising,  until  I  .fou-nd  that  the  scyphistomas  were 
multiplying  freely  by  budding,  in  a  manner  to  be  described  later  on.  During  my  second 
visit  I  found  this  species  as  abundant  as  ever  in  this  locality,  and  I  also  found  a  number  of 
adult  specimens  in  several  of  the  small  shallow  lagoons  among  the  mangroves  in  the  rear 
of  Port  Royal.  But  these  were  all  females,  and  it  was  still  impossible  to  obtain  males 
or  eggs  that  would  develop. 

1  Although  Fewkes  ('82)  identifies  his  Cassiopea  frondosa  Lamarck,  of  Key  West  and  the  Tortugas,  with  Polyclonia 
frondosa  Ag.,  it  is  nevertheless  a  true  Cassiopea,  not  a  Polyclonia. 


CASSIOPEA   XAMACHANA.  193 

Full-grown  medusae  could  be  kept  in  good  condition  in  aquaria  for  a  number  of  days, 
and  could  be  kept  alive  for  weeks;  while  the  young  medusae  and  scyphistomas  would 
thrive  there  an  indefinite  time,  if  there  were  a  little  pond  ooze  at  the  bottom  of  the 
aquarium  and  the  water  were  changed  twice  a  day.  Indeed  the  growth  and  multiplication 
of  the  scyphistomas  would  proceed  actively  under  these  conditions.  By  keeping  the  larvae 
in  shallow  dishes  I  was  able  to  watch  the  whole  course  of  non-sexual  development ;  but  the 
development  from  eggs  remains  unknown  to  me  because  of  the  impossibility  of  finding  any 
that  would  develop.  It  was  not  until  a  few  days  before  we  left  Jamaica  in  1891  that  I 
discovered  the  habit  that  the  very  young  free-swimming  larvae  have  of  hiding  beneath  the 
bits  of  bark  and  the  like  to  which  the  scyphistomas  in  the  aquarium  were  attached,  and 
therefore  the  greater  part  of  my  work  on  the  early  stages  of  development  was  done  during 
the  second  expedition. 

After  a  few  words  concerning  technique  I  shall  begin  with  a  systematic  description  of 
the  species,  followed  by  an  account  of  the  anatomy  of  the  adult,  and  the  remaining  part 
of  the  paper  will  contain  what  I  have  learned  of  the  development  from  the  observation  of 
the  living  animals  while  in  Jamaica,  and  by  the  study  of  sections  of  preserved  material, 
carried  on  chiefly  at  the  Biological  Laboratory  of  the  Johns  Hopkins  University,  but  in 
part  also  at  the  Marine  Biological  Laboratory  of  Woods  Hole  and  at  the  Biological 
Laboratory  of  the  U.  S.  Fish  Commission  in  the  same  place. 

I  wish  to  express  my  thanks  to  Professor  W.  K.  Brooks  for  the  advice  and  encourage- 
ment that  he  gave  me  while  I  was  doing  this  work  as  one  of  his  students,  and  I  am  also 
indebted  to  Professor  C.  0.  Whitman,  to  the  Hon.  George  M.  Bowers,  and  to  Professor 
H.  C.  Bumpus  for  the  many  courtesies  received  while  at  Woods  Hole. 


TECHNIQUE. 

For  the  preservation  of  the  very  young  larvae  a  one  quarter  saturated  solution  of 
picric  acid,  with  2%  of  sodium  chloride  added,  gave  good  results.     Erlicki's  fluid  with  the 
same  addition,  and  j%  osmic  acid  followed  by  Erlicki's  fluid,  did  fairly  well  for  scyphis- 
tomas, but  the  best  specimens  obtained  were  those  killed  in  the  following  mixture : 
10%  solution  copper  sulphate  100  c.  c. 

saturated  solution  corrosive  sublimate  10  c.  c. 

As  soon  as  they  were  killed,  the  specimens  were  placed  in  5%  bichromate  of  potassium 
and  left  there  until  hardened,  after  which  they  were  washed  in  35%  alcohol  containing  a 
trace  of  hydrochloric  acid  and  preserved  in  70%  alcohol.  Excellent  preparations  of  the 
medusae  were  obtained  by  this  same  method,  and  Flemming's  fluid  also  gave  good  results. 


194  ROBERT   PAYNE   BIGELOW  ON 


SYSTEMATIC  PART. 

Genus  Cassiopea  PERON  and  LESUEUR  (1809).  —  This  genus,  as  limited  by 
Haeckel  ('80) ,  may  be  defined  as  follows :  Discomedusae  without  tentacles  and  without  a 
central  mouth  opening ;  provided?  instead  of  the  latter,  with  numerous  oral  funnels  at- 
tached to  the  ventral,  or  axial,  side  of  the  eight  oral  arms,  which  are  pinnately  or  tricho- 
tomously  branched,  have  a  subcylindrical,  or  subconical,  gelatinous  support  continuous 
to  the  tips  of  the  principal  branches,  are  provided  with  numerous  chtb-shajjed  vesicles 
among  the  oral  funnels,  and  are  without  appendages  on  the  dorsal,  or  abaxial,  side ; 
also  with  four  interradial  gonads  in  the  aboral  wall  of  the  four  separate  subgenital  cav- 
ities; sixteen  marginal  sense  organs  (rhopalia);  and  thirty-two  radial  canals  connected 
by  a  network  of  anastomosing  branches. 

For  the  sake  of  clearness  this  definition  is  made  to  include  the  characters  of  the 
family  Toreumidae  Haeckel,  to  which  this  genus  belongs,  and  the  purely  generic  charac- 
ters are  italicized. 

Cassiopea  xaxnachana.1 

Cassiopea  xamachana  BIGELOW,  Zool.  Anzeiger,  no.  393,  1892,  pp.  212-214. 

(?)    C.frondosa  FEWKES,  Bull.  mus.  comp.  zool.,  vol.  9,  no.  7,  1882,  pp.  254-259. 

Diagnosis.  —  A  Cassiopea  with  a  disc-like  umbrella,  concave  on  the  aboral  side ; 
when  regular,  with  eighty  short  and  obtuse  marginal  lobes  separated  by  deep  grooves  on 
the  surface  of  the  exumbrella  (in  each  of  the  sixteen  parameres  three  velar  lobes  between 
two  ocular  ones) ;  white  markings  on  the  exumbrella,  consisting  of  a  circular  band  with 
a  diameter  somewhat  greater  than  that  of  the  concavity,  within  this  sixteen  oval  or  elip- 
tical  spots  lying  in  the  radii  of  the  rhopalia,  and  on  the  outer  side  eighty  marginal  spots, 
one  for  each  marginal  lobe ;  oral  arms  rounded  and  slender,  never  angular,  exceeding  the 
radius  of  the  umbrella  by  at  least  one  half  of  its  length,  and  bearing  nine  to  fifteen 
primary  branches  which  are,  in  turn,  copiously  branched,  giving  the  whole  appendage  a 
spatulate  outline ;  very  numerous  small  oval  vesicles  attached  at  the  axils  of  the  small 
branches  and  thickly  massed  upon  the  oral  disc  of  adult  females,  and  many  small  and  a 
few  large,  flattened,  linear  vesicles  attached  one  at  the  axil  of  each  of  the  larger  branches 

1  This  name,  suggested  by  Professor  Brooks,  must  stand  as  printed  in  the  preliminary  description  of  the  species, 
according  to  the  current  rules  of  nomenclature,  followed  by  the  Boston  Society  of  Natural  History.  But  it  should  have 
been  written  xamaycana,  from  Xamayca  (the  x  is  pronounced  like  ch  in  the  German  ach),  the  Indian  name  for  the  island  of 
Jamaica,  as  written  by  the  early  Spanish  historians  (see  Herrera,  Novi  orbis  pars  duodecima,  sive  descriptio  Indiee  occiden- 
talis,  1024  ;  also  Encycl.  Brit.,  9th  ed.,  article,  Jamaica).  The  form  Xaymaca  given  by  Bridges,  Annals  of  Jamaica,  1827, 
and  followed  by  several  subsequent  authors,  is  probably  a  misprint. 


CASSIOPEA  XAMACHANA.  195 

and  to  the  canals  on  the  oral  disc,  the  thirteen  largest  vesicles  being  one  at  the  axil  of 
the  largest  branch  on  each  arm  and  one  at  each  junction  of  the  canals  on  the  oral  disc; 
oral  funnels  entirely  wanting  on  the  oral  disc  in  adult  females,  but  present  in  immature 
specimens. 

S2)ecial  description.  —  A  detailed  account  of  the  anatomy  of  this  species  will  be  given 
in  the  anatomical  portion  of  this  paper.  It  is  intended  here  to  call  attention  merely  to 
the  features  that  distinguish  our  species  from  its  nearest  allies.  Cassiojjea  xamachana 
resembles  very  closely  two  medusae  that  inhabit  the  Red  Sea  and  Indian  Ocean,  Cassioftea 
andromeda  Eschscholtz  and  C.  polypoides  Keller  ('83),  but  it  seems,  nevertheless,  to  be 
distinct  from  either. 

Upon  comparison  with  the  descriptions  of  Cassiopea  andromeda  given  by  Tilesius 
('29),  Haeckel  ('79),  and  Vanhoft'en  ('88),  and  with  the  figures  of  Tilesius  ('29)  and 
Forskal  (1776) ,  C.  xamachana  appears  to  differ  from  this  species  in  the  following 
particulars  :  The  exumbrella  is  not  merely  flat,  but  is  concave ;  besides  the  ninety-six  white 
spots  on  the  exumbrella,  there  is  a  broad  circular  band  of  white  more  or  less  connected 
with  all  of  the  marginal  spots  (Fig.  35),  the  oral  arms  are  more  thickly  branched  and  are 
longer,  exceeding  by  one  half  to  two  fifths  the  radius  of  the  umbrella,  instead  of  being 
only  one  third  longer ;  moreover  the  arms  have  none  of  the  flattened  appearance  figured 
by  Tilesius  and  mentioned  by  Haeckel. 

C.  xamachana  differs  from  C.  polypoides  in  having  more  slender  oral  arms,  with  five 
to  seven  pairs  of  branches  instead  of  three,  and  with  fewer  very  large  vesicles,  and  these 
apparently  not  so  large  and  always  flattened.  The  color  pattern  in  the  two  species  is 
nearly  the  same,  except  that  in  C.  xamachana  the  three  white  spots  on  the  three  velar 
lobes  of  each  paramere  are  seldom  widely  separated  from  the  circuLar  band  of  white. 
The  colors  in  the  pattern,  however,  differ  considerably  in  the  two  species.  The  ground 
color  in  C.  xamachana  is  never  light  brown,  but  is  always  much  darker,  a  greenish  brown, 
usually  with  a  distinct  shade  of  blue  on  the  subumbrella.  The  large  oral  vesicles  are 
never  sky-blue,  rose-colored  nor  white,  but  are  yellowish  green,  often  with  a  bluish  green 
stripe ;  and,  while  the  margins  of  the  oral  funnels  are  deep  brown,  they  are  always  fringed 
with  the  white  digitella. 

C.  xamachana  is  easily  distinguished  from  C.  ornata  Haeckel  by  the  presence  of 
large  oral  vesicles  and  by  the  more  extensive  branching  of  the  arms ;  and  it  differs  from 
C.  mertensii  Brandt  ('38),  C.  depressa  Haeckel  (?80),  and  C.  jricta  Vanhoffen  ('88),  in  the 
number  of  marginal  lobes  on  the  umbrella.  C.  ndrosia  Agassiz  and  Mayer  ('99)  differs 
also  in  number  of  marginal  lobes  and  in  coloring.  Fewkes  ('82)  has  described  a  medusa 
from  Key  West  and  the  Tortugas  under  the  name  "  Cassiopea  frondosa  Lamarck,"  which 
he  regards  as  identical  with  Polyclonia  frondosa  Agassiz.  From  the  description  given  by 


196  ROBERT    PAYNE    BIGELOW   ON 

Fewkes  it  is  impossible  to  identify  his  species  positively.  But  a  comparison  of  his 
figures  with  living  specimens  of  both  sexes  of  P.frondosa  shows  at  once  that  the  two 
species  are  distinct ;  while  a  comparison  with  C.  xamachana  shows  so  close  a  resemblance 
that  I  am  inclined  to  think  that  Fewkes  has  discovered  one  of  the  varieties  of  our  species, 
described  in  the  next  section.  Not  only  is  P.  frondosa  perfectly  distinct  from  C.  xama- 
chana, but  I  think  we  are  justified  in  retaining  the  former,  for  the  present  at  least,  in  a 
separate  genus ;  and  there  can  be  little  doubt  that  Lamarck's  Cassiopea  frondosa  dwell- 
ing in  the  "Ocean  of  the  Antilles"  with  its  " margine  decem-lobata"  is  none  other  than 
Agassiz's  Polyclonia  frondosa.  Therefore,  even  if  it  should  be  proved  that  the  form 
described  by  Fewkes  is  the  same  as  the  subject  of  the  present  memoir,  the  name  that  I 
have  given  to  it  will  hold,  nevertheless,  as  the  designation  of  the  species. 

Variations.  —  If  we  compare  the  average  dimensions  of  various  organs,  expressed  in 
thousandths  of  the  diameter,  with  the  maxima  and  minima,  as  may  be  done  by  examining 
the  third,  fourth,  and  fifth  columns  in  Table  1,  p.  201,  it  becomes  evident  that  there  is  a 
very  considerable  amount  of  variation  in  the  relative  size  of  parts  of  C.  xamachana. 

In  the  oral  arms,  not  only  does  the  relative  size  vary,  but  the  number  and  the 
arrangement  of  the  branches  are  both  variable.  Moreover  this  variability  exists  between 
the  different  individuals.  In  nineteen  specimens  examined  the  maximum  number  of 
branches  found  on  one  arm  was  sixteen,  the  minimum  nine,  and  the  greatest  difference 
on  any  one  individual  was  four. 

The  most  striking  variations  in  C.  xamachana,  however,  are  to  be  found  in  the 
structures  at  the  margin  of  the  umbrella.  These  are  highly  variable  in  this  species,  and 
have  been  found  to  be  variable,  although  to  a  less  extent,  in  other  medusae.  It  is 
unfortunate,  therefore,  that  in  his  beautiful  systematic  work  on  the  medusae  Haeckel 
should  have  found  himself  forced  to  distinguish  the  genera  chiefly  by  differences  in  the 
marginal  structures.  He  himself  notes  the  variability  in  the  number  of  parameres  of 
Polyclonia  frondosa.  Agassiz  and  Mayer  ('99)  found  in  one  specimen  of  C.  ndrosia 
eighteen  rhopalia,  and  in  another  twenty-two. 

The  number  of  rhopalia  was  counted  in  twenty-seven  specimens  of  C.  xamachana.  Of 
these  ten  were  found  to  have  sixteen,  the  typical  number  for  the  genus,  and  twelve  had 
more  than  sixteen,  three  having  seventeen,  and  three  more,  eighteen.  The  largest 
number  on  one  individual  was  twenty-three.  There  were  five  specimens  with  fewer  than 
sixteen  rhopalia,  but  only  two  had  less  than  fifteen,  and  both  of  these  showed  correlated 
abnormalities  in  the  mouth  parts  and  subgenital  cavities.  One  had  fourteen  rhopalia,  four 
oral  arms,  and  two  subgenital  cavities  and  gonads.  The  other  had  ten  rhopalia,  only  five 
oral  arms,  with  three  oesophageal  canals  leading  from  the  stomach  to  the  canal  system  of 
the  arms,  and  three  normal  subgenital  cavities  and  one  very  small  vestigial  one  (Fig.  A.) . 


CASSIOPEA   XAMACHANA.  197 

Redundancy  of  mouth  parts  is  not  nearly  as  common  as  of  the  marginal  structures. 
Only  two  cases  were  observed.  One  specimen  with  an  additional  pair  of  oral  arms  in  one 
interradius  had  seventeen  rhopalia,  The  other  had  eleven  arms,  with  five  subgenital 
spaces  and  gonads,  and  this  one  had  twenty-two  rhopalia.  On  the  other  hand,  five  speci- 
mens were  found  with  twenty  or  more  rhopalia,  and  perfectly  normal  mouth  parts. 

It  will  be  seen,  then,  that  the  number  of  rhopalia,  which  has  been  taken  as  the 
principal  generic  character  in  the  group,  is  a  highly  variable  one.  The  number  of 


Fig.  A.  Section  through  the  stomach  of  a  specimen  with  only  10  rhopalia  and  5  oral  arms,  to  show  the  abnormal 
arrangement  of  gonadia  and  oesophageal  canals.  In  the  region  marked  a  the  margin  of  the  umbrella  presents  a  wide 
space  in  which  there  are  no  rhopalia.  go  =  gouad.  For  explanation  of  the  other  lettering  see  Explanation  of  Plates. 

marginal  lobes  in  each  paramere  has  been  taken  as  one  of  the  principal  specific  characters, 
and  this  is,  likewise,  highly  variable.  The  variation  consists  principally  in  the  interpolation 
of  a  small  secondary  lobe  between  two  typical  ones.  Even  in  a  regular  and  typical 
specimen,  such  as  is  shown  in  Fig.  35,  the  position  that  would  be  taken  by  these  secondary 
lobes  is  indicated  by  small  ridges  on  the  dorsal  surface.  A  specimen  with  a  large  number 
of  rhopalia  is  as  likely  to  have  the  marginal  lobes  in  each  paramere  arranged  typically  as 
one  having  a  smaller  number.  Conversely,  a  specimen  with  fifteen  to  seventeen  parameres 
is  as  likely  as  not  to  vary  from  the  typical  form.  The  variation  may  consist  in  the  addi- 
tion of  two  secondary  lobes  in  the  paramere,  the  addition  of  four  lobes,  or  in  a  quite 
irregular  arrangement ;  and  this  modification  may  affect  all  of  the  parameres  alike  or  only 
a  portion  of  them. 

Throughout  all  of  these  modifications  of  the  margins  there  is  manifested  a  constant 
regard,  as  it  were,  for  the  symmetry  of  the  parts.  It  is  very  seldom  that  an  additional 
rhopalium  appears  as  if  attached  fortuitously  in  some  irregular  way.  Almost  always  either 
it  is  in  the  midst  of  an  entirely  new  paramere  or  else  there  is  a  distinct  line  of  symmetry 
running  between  two  adjacent  rhopalia  that  evidently  correspond  to  an  originally  single 
one.  In  other  words,  a  paramere  has  been  incompletely  doubled,  and  the  two  parts  are 


198  ROBERT   PAYNE   BIGELOW   ON 

bilaterally  symmetrical  to  one  another.  We  find  all  degrees  of  this  doubling  in  the  adult 
from  a  double-headed  rhopalium  1  to  two  complete  parameres,  and  the  same  process  may 
be  seen  in  the  forked  tentacles  frequently  found  in  the  larvae  (Figs.  14  and  21,  x) .  With 
the  exception  of  the  forked  tentacle  and  the  double-headed  rhopalium,  these  stages  of 
duplication  are  well  represented  at  ?«,  w,  x,  y  and  z  in  Fig.  30. 

The  radially  arranged  stripes  and  spots  on  the  exumbrella,  which,  with  a  circular 
band,  form  the  color  pattern  described  in  the  next  section,  vary  in  number  with  the 
rhopalia  and  marginal  lobes.  But  when  two  rhopalia  are  close  together  there  may  be 
only  one  corresponding  rhopalial  stripe,  and  it  will  then  occupy  a  position  intermediate 
between  the  two.  For  example,  in  the  specimen  mentioned  before  as  having  only  ten 
rhopalia,  two  of  the  rhopalia  were  very  close  together  and  there  was  but  one  rhopalial 
stripe  corresponding  to  them.  The  other  rhopalia  were  evenly  spread,  except  that  they 
were  absent  from  one  rather  wide  section  of  the  circle.  The  rhopalial  stripes,  nine  in  all, 
were  placed  in  a  corresponding  manner,  and  were  absent  from  the  corresponding  area. 

There  is  also  a  wide  degree  of  variation  in  the  extent  of  fusion  between  the  circular 
band  and  the  marginal  spots.  The  spots  on  the  velar  lobes  are  usually  not  fused  to  the 
circular  band  in  young  specimens,  and  they  frequently  remain  distinct  in  adults.  It 
was  found,  however,  that  this  is  more  usually  true  of  specimens  from  the  Salt  Pond  than 
of  those  from  Port  Royal.  I  thought  that  I  could  see,  also,  correlated  differences  in  the 
'  sizes  of  certain  of  the  mouth  parts,  and  I  was  thus  led  to  inquire  if  there  were  a  division 
here  of  the  species  into  two  races.  For  this  purpose  Table  2,  p.  201,  was  constructed. 
From  this  it  will  be  seen  that  the  specimens  from  the  Salt  Pond  (var.  A)  have  on  the 
average  longer  oral  arms  and  shorter  vesicles  than  the  ordinary  specimens  from  Port 
Royal  (var.  B) ,  while  the  stomach  is  of  the  same  size  in  the  two  groups.  Whether  these 
slight  differences  are  in  any  way  connected  with  the  probable  difference  in  density  of  the ' 
water  in  the  two  localities,  experiment  alone  can  determine. 

In  the  third  column  of  this  table  dimensions  are  given  of  some  specimens  from  Port 
Royal  (var.  C)  that  are  so  different  from  the  rest  that  they  might  be  regarded  as  of  a 
distinct  species.4  Suspicion  of  their  being  merely  sports  is  aroused,  however,  by  the  fact 
that  only  two  specimens  (female)  were  found  living  among  a  large  number  of  the 
usual  form. 

The  most  striking  peculiarity  of  these  two  specimens  was  the  great  number  (forty 
to  fifty)  of  uniformly  large  oral  vesicles,  two  to  four  centimeters  in  length,  scattered  over 

1  Fewkes,  ('82)  has  observed  similar  double-headed  rhopalia,  and  it  is  on  account  of  the  variability  of  the  marginal 
structures  that  he  regards  Polyclonia  as  merely  an  abnormal  Cassiopea. 

1  It  is  possible  that  this  variety  may  be  the  same  as  Cassiopea  frondosa  Lamarck  of  Fewkes,  although  his  figures  do  not 
show  any  large  vesicles  on  the  proximal  parts  of  the  oral  arms. 


CASSIOPEA  XAMACHANA.  199 

the  whole  extent  of  the  mouth  parts.  Among  them  the  central,  radial,  and  primary 
vesicles  were  hardly  distinguishable,  although  so  easily  recognized  by  their  greater  size 
in  the  typical  form  of  the  species. 

Another  peculiarity  was  a  projection  of  the  mesogloea  on  the  oral  side  of  each 
subgenital  osteum,  so  that  the  interradial  diameter  of  the  oral  disc  was  considerably  longer 
than  the  radial  diameter,  as  shown  in  the  table.  These  specimens  presented  also  some 
peculiarities  of  coloring,  which  will  be  noted  in  the  next  section. 

Color. — The  coloring  of  this  semi-transparent  animal  consists  of  certain  white  mark- 
ings, together  with  shadings  of  subdued  tints  of  brown,  green  and  blue,  that  are  often 
very  beautiful. 

If  we  turn  the  aboral  side  (Fig.  35)  of  the  medusa  toward  us  we  find  often  a  brown- 
ish band  encircling  the  disc  at  the  periphery  of  the  concavity  and  shading  off  gradually 
on  both  sides.  Deeper  within  the  mesogloea  there  is  a  much  wider  white  circular  band 
extending  under  the  brownish  one ;  and  white  bands,  or  spots,  extend  in  a  radial  direction 
outward  from  this  along  the  marginal  ridges.  There  is  one  spot  to  each  ridge,  and  it 
reaches  nearly  to  the  tip  of  the  marginal  lobe.  The  bands  on  the  rhopalial  lobes  are  inter- 
rupted, however,  by  a  roughly  circular,  transparent  area  over  each  rhopalium ;  and  in 
many  specimens,  especially  young  ones,  the  interrhopalial  (velar)  spots  are  not  fused  with 
the  circle.  On  the  inner  side  of  the  circular  band  of  white  there  is  a  circle  of  large  white 
spots,  "rhopalial  spots,"  or  stripes,  that  lie  deep  in  the  substance  of  the  exumbrella  and 
are  visible  through  the  mesogloea,  one  in  the  radius  of  each  rhopalium.  The  spot  is 
elliptical  in  outline,  and  extends  from  the  white  band  to  a  point  about  two  fifths  of  the 
distance  between  the  periphery  of  the  concavity  and  the  edge  of  the  stomach.  These 
spots,  while  usually  continuous  with  the  band,  like  the  marginal  spots,  are  not  always  so. 

At  the  centre  of  the  umbrella  the  stomach  and  subgenital  cavities  may  be  seen 
through  the  mesogloea  as  a  reddish  brown  circular  area  with  a  diameter  of  about  one 
fourth  of  the  total  diameter  of  the  disc ;  while  surrounding  the  stomach  there  is  a  deep 
blue  halo  with  points  that  extend  outward  between  the  last-mentioned  bands  of  white. 

Now  if  the  animal  be  allowed  to  return  to  its  usual  position,  the  subumbrellar  surface 
will  be  found  to  be  pretty  evenly  stippled  by  the  greenish  brown  cells  in  the  mesogloea. 
Apparently  beneath  this  stippling  there  is  a  blue  pigment  forming  a  circle  around  the 
margin  of  the  stomach  and  extending  outward  in  broad  bands,  one  along  each  interrho- 
palial radius,  nearly  or  quite  to  a  large,  more  or  less  distinct  patch  of  blue,  that  lies  close 
to  the  margin  between  every  two  rhopalia.  The  radial  canals,  and  the  fine,  connecting 
network  of  tubes,  appear  as  rather  indistinct,  opaque,  white  lines. 

The  mesogloea  of  the  oral  arms  is  transparent  and  colorless,  except  for  an  opaque 
white  stripe  beneath  the  dorsal  surface  of  each  arm.,  of  the  same  character  as  the  white 


200  ROBERT    PAYNE    BIGELOW   ON 

markings  of  the  umbrella.  There  is  a  similar  stripe  on  the  dorsal  side  of  each  of  the 
larger  branches  which  may,  or  may  not,  be  continuous  with  the  stripe  on  the  main  stem. 
The  bases  of  the  oral  funnels  are  of  a  delicate  blue  color,  which  often  extends  to  the 
brachial  canal.  The  margin  of  each  funnel  is  a  deep  brown,  that  shades  off  over  the 
blue ;  while  the  small  tentacles,  or  digitella,  that  spring  from  this  margin  are  pure  white. 
The  larger  tongue-shaped  vesicles  on  the  arms  and  oral  disc  have  a  greenish  yellow  color 
with  a  bluish  green  longitudinal  stripe.  The  smaller  vesicles  on  the  arms  are  colored  in 
a  similar  way  and  are  inconspicuous,  but  the  cluster  of  very  small  vesicles  that  occupy  the 
greater  part  of  the  oral  disc  has  a  very  different  appearance,  being  lightly  tinted  by  line 
reddish  brown  pigment  spots. 

The  two  specimens  that  I  have  called  variety  C,  are  somewhat  differently  colored. 
The  markings  are  yellowish  white.  The  circular  white  band  is  indistinct.  The  rhopalial 
bands  are  interrupted  at  the  margin  of  the  concavity  of  the  exumbrella,  and  stop  short 
about  half  a  centimeter  from  the  rhopalial  hood.  At  the  margin  of  the  umbrella  there  is 
a  white  spot  on  each  rhopalial  lobe  and  a  strap-shaped  spot  on  each  velar  lobe.  The 
centre  of  the  umbrella  is  whitish  and  opaque,  so  that  the  stomach  does  not  show  through. 
The  oral  arms  are  translucent,  milky  white  tinged  with  brown,  and  without  distinct  white 
markings,  except  on  the  dorsal  side  of  the  principal  branches.  The  large  oral  vesicles 
are  yellow  and  greenish  yellow,  with  a  brown  centre. 

Size.  —  The  diameter  of  the  largest  specimen  found  is  24  cm.,  while  the  smallest 
specimen  that  contained  eggs  measured  6.5  cm.  The  average  diameter  of  twenty-three 
adult  specimens  was  13.7  cm.  The  relative  sizes  of  the  parts  are  exhibited  in  the  follow- 
ing tables.  Table  1  shows  what  may  be  regarded  as  the  normal  proportion  for  the  species, 
though,  to  be  sure,  some  of  the  measurements  were  made  only  on  Port  Royal  specimens. 
Some  of  the  dimensions  were  measured  on  a  smaller  number  of  specimens,  and  for  these 
the  average  diameter  of  the  umbrella  of  the  specimens  on  which  these  measurements 
were  made  is  given  separately  to  show  the  correct  proportions.  Table  2  furnishes  a 
means  of  comparing  the  proportions  in  the  three  varieties. 


CASSIOPEA   XAMACHANA. 


201 


TABLE   1.      DIMENSIONS   OF   SPECIMENS   FROM   BOTH   SALT   POND  AND   PORT  ROYAL 

(VARIETIES  A   AND   S.) 


Number  of 
specimens 
measured 

Average  di- 
mensions in 
centimeters 

Average  dimensions 
in  thousandths  of 
average    d  iameter 

Maximum               Minimum 

(In    thousandths    of    diameter 
unless  otherwise  noted) 

Remarks 

Diameter  of  umbrella 

21 

14.33 

1000 

24  cm. 

9  cm. 

Length  of  arms  meas- 
ured from  centre  of 

Salt  Pond  and 

oral  disc 
Length     of      central 
vesicle 
Length     of    primary 
vesicle 

21 
21 
21 

11.21 

2.71 
1.82 

782 
189 
126 

888 
287 
190 

642 
103 
71 

Port        Royal 
specimens  tak- 
en together. 

Diameter  of  umbrella 
Length      of      radial 
vesicle 

10 
10 

15.79 
3.01 

1000 
190 

24  cm. 
250 

12  cm. 
117 

Port        Royal 
only. 

Diameter  of  umbrella 

11 

13.02 

1000 

16.3  cm. 

6.3  cm. 

Salt  Pond  and 

Diameter  of  stomach 

11 

4.22 

311 

333 

292 

Port  Royal. 

Diameter  of  umbrella 

3 

18.66 

1000 

24  cm. 

15  cm. 

Thickness  of  umbrella 
Total  depth 

3 
3 

1.33 
3.59 

71 
191 

73 
212 

70 
173 

Port  Royal. 

Diameter  of  umbrella 
Diameter  of  oral  disc 

2 

2 

20.50 
8.00 

1000 
390 

24  cm. 
441 

17  cm. 
354 

Port  Royal. 

TABLE   2.       AVERAGE   DIMENSIONS   OF    THE   THREE    VARIETIES,    GIVEN   IN  THOUSANDTHS 
OF  THE   AVERAGE   DIAMETER   OF  THE    UMBRELLA. 


Variety  A—  Salt  Pond 

Variety  B—  Port  Royal 

Variety  C—  Port  Royal 

Length  of  arms 
Length  of  central  vesicle 
Radial  vesicle 

850 
157 

715 

217 
190 

818 
163 

Primary  vesicle 
Diameter  of  stomach 

112 

298 

138 
311 

167 
322 

Thickness  of  umbrella 



71 

80 

Total  depth 
Radial  diameter  of  oral  disc 



191 
390 

213 
394 

Interradial  diameter  of  oral  disc 



390 

470 

Locality.  —  Great  Salt  Pond,  and  mangrove  swamps  ("  The  Lakes")  in  the  rear  of 
Port  Royal,  Jamaica. —  BIGELOW. 

(?)  Moat  outside  Fort  Jefferson  on  Garden  Key,  Tortugas  Islands,  and  Mangrove 
Keys,  near  Key  West,  Florida.  —  FEWKES. 


202  ROBERT   PAYNE   BIGELOW   ON 


ANATOMY. 

Form  of  the  Body.  —  To  one  who  is  familiar  with  the  cyaneas,  aurelias,  and  the 
like,  of  our  northern  coast,  the  shape  of  this  medusa  appears  very  strange.  The  aboral, 
or  exumbrellar  surface  (Fig.  35),  instead  of  being  convex  in  Cassiopea  xamnchana,  as 
it  is  in  the  great  majority  of  medusae,  is  concave  when  the  animal  is  at  rest,  except  for  a 
slight  convexity  over  the  stomach,  and  except  in  the  region  of  the  thinner  marginal  part 
of  the  umbrella,  where  also  it  is  convex.  The  surface  of  the  subumbrella,  on  the  other 
hand,  is  convex,  except  in  this  same  thinner  marginal  area,  where  it  is  in  turn  concave. 
The  umbrella  thickens  very  gradually  from  its  margin  to  the  centre,  and  the  elevations 
and  depressions  of  its  surface  have  very  gentle  slopes,  so  that  its  general  shape  is  much 
nearer  that  of  a  flat  disc  than  the  dome-like  form  of  most  medusae  (Fig.  35) . 

A  circular  column  arises  from  the  centre  of  the  oral  surface  of  the  umbrella.  It  is 
broad,  but  very  short;  and  a  few  millimeters  from  the  umbrella  it  loses  its  circular 
outline,  owing  to  eight  stout  arms  that  spring  from  it  at  regular  intervals  (Fig.  34) . 
These  are  smooth  and  rounded,  except  along  a  line  on  the  oral  side,  where  they  bear 
the  fringe  of  oral  appendages,  and  they  are  long  and  much  branched.  This  column  is 
the  oral  disc,  and  its  arms  the  oral  arms. 

The  Structure  of  the  Mesogloea.  —  By  far  the  greater  part  of  the  mass  of  the  oral 
arms  and  disc,  as  well  as  the  umbrella,  is  composed  of  a  firm,  elastic,  gelatinous 
substance,  the  mesogloea,  and  it  is  to  this  that  the  shape  of  the  body  is  due. 

The  description  given  by  Keller  ('83),  of  the  structure  of  the  mesogloea  in  C.  poly- 
poides  would  apply  almost  equally  well  to  our  species.  The  mesogloea  consists  of  a 
hyaline  matrix,  in  which  are  imbedded  certain  fibres  and  three  kinds  of  cellular  elements. 
Most  of  the  fibres  appear  to  be  analogous  to  connective  tissue  fibres,  and  take  a  general 
course  through  the  mesogloea  at  right  angles  to  the  surface.  Others  seem  to  be  proto- 
plasmic. At  any  rate,  they  may  be  observed  to  proceed  from  the  star-shaped  cells  that 
are  scattered  throughout  the  jelly. 

The  cellular  elements  are  :  the  star-shaped  cells,  just  mentioned;  vesicular  bodies, 
found  in  certain  restricted  localities ;  and  the  green  cells,  which,  as  it  will  be  shown  later, 
are  symbiotic  plants. 

The  star-shaped  cells  remind  one  of  osteoblasts,  and  are  probably  analogous  to  them, 
in  that  they  are  concerned  in  the  formation  of  the  jelly.  Hamann  ('8l)  has  called 
them  colloblasts.  They  are  small,  often  somewhat  elongated,  and  have  a  well-marked 
nucleus. 


CASSIOPEA   XAMACIIANA.  203 

The  vesicular  bodies  give  rise  to  the  white  markings  that  were  mentioned  in  the 
description  of  the  species.  These  vesicles  are  much  larger  than  the  colloblasts.  Each 
one  seems  to  be  made  up  of  a  wall  of  exceedingly  minute  refractile  granules,  surrounding 
a  clear  space.  That  this  body  is  a  cell,  however,  is  shown  by  the  presence  of  a  nucleus 
pressed  closely  against  one  side. 

The  green  cells,  or  zoanthelae,  are  widely  distributed  throughout  the  mesogloea,  but 
are  most  abundant  in  the  umbrella.  They  are  not  infrequently  found  imbedded  in  the 
endodermal  epithelium.  The  living  cells  have  a  greenish  brown  color,  which  they 
impart  to  the  animal  as  a  whole.  They  are  of  considerable  size,  are  globular, 
without  projections  of  any  kind,  and  are  generally  to  be  found  in  clusters  of  two  or  more 
(za,  Figs.  52,  56,  and  63) .  Each  one  contains  a  nucleus  and  numerous  granular  bodies, 
and  apparently  is  surrounded  by  a  cell  wall ;  but  the  latter  is  hard  to  distinguish  from 
the  edge  of  the  adjacent  matrix. 

Keller  thought  that  similar  bodies  in  C.  polypoides  could  not  be  algae,  because  he 
failed  to  find  any  evidence  of  a  cellulose  cell  wall.  He  regarded  them,  therefore,  as 
essential  elements  of  the  "  mesoderm." 

In  those  of  my  specimens,  however,  which  have  been  killed  in  Erlicki's  fluid  and 
stained  with  borax  carmine,  the  nucleus  of  these  cells  is  found  to  be  red,  while  the  gran- 
ular contents  of  the  cell  are  bright  green,  and  there  are  often  one  or  two  green  bodies 
present  that  are  as  large  or  larger  than  the  nucleus.  They  have  all  the  appearance  of 
chlorophyl  bodies,  and  it  is  well  known  that  the  chlorophyl  of  some  algae  is  not  readily 
removed  by  alcohol.  Moreover,  in  teased  preparations  treated  with  iodine  solution  these 
cells  are  found  to  be  filled  with  granules  that  quickly  turn  deep  blue,  —  evidently  starch. 
The  test  for  cellulose  with  iodine  followed  by  sulphuric  acid,  gave,  however,  unsatisfac- 
tory results.  The  outline  of  the  cell  would  become  distinctly  darker,  but  not  recognizably 
blue.  In  the  same  way  with  chloriodide  of  zinc,  a  very  marked  reaction  for  starch  was 
obtained,  the  granules  becoming  almost  black ;  but  so  long  as  the  object  was  viewed 
by  direct  transmitted  light,  no  reaction  for  cellulose  could  be  detected  with  certainty. 
On  the  other  hand,  when  the  light  was  thrown  upon  the  object  obliquely  by  means  of  a 
condenser  with  a  central  diaphragm,  the  effect  was  quite  different.  The  starch  granules 
became  a  deep  ultramarine,  and  the  parts  of  the  cell  not  occupied  by  the  starch  appeared 
distinctly  violet,  showing  without  doubt  the  presence  of  cellulose. 

Both  starch  and  cellulose,  as  well  as  some  form  of  chlorophyl,  having  been  demon- 
strated in  them,  there  can  be  no  further  question  that  the  green  cells  in  Cassiopea  are 
symbiotic  algae. 

The  Oral  Arms  and  their  Branches.  —  The  eight  oral  arms  (Fig.  34)  arise  from 
the  central  oral  disc  at  about  equal  intervals;  and  when  an  arm  is  extended,  the  distance 


204  ROBERT   PAYNE   BIGELOW   ON 

from  the  centre  of  the  oral  disc  to  the  tip  of  the  arm  about  equals  three  quarters  of  the 
diameter  of  the  umbrella.  But  the  arms  are  very  contractile,  and  may  be  shortened  to 
half  this  length.  The  arms  are  slender  and  graceful  in  shape,  the  mesogloea  tapering 
very  gradually  to  the  tips  of  the  finest  branches.  The  branches  are  arranged  alternately. 
The  largest  one,  which  is  the  first  formed,  is  at  a  point  about  two  thirds  the  length  of 
the  arm  from  its  base.  From  this  point  the  branches  decrease  in  size  gradually  toward 
the  base  of  the  arm,  and  more  rapidly  toward  the  apex.  The  general  outline  of  the 
arm,  therefore,  including  its  branches,  is  roughly  spatulate. 

The  Oral  Funnels  and  Brachial  Appendages.  —  Just  below  the  surface  of  the 
oral  side  of  each  arm  there  is  a  longitudinal  tube,  the  brachial  canal,  that  ramifies  to 
each  branch,  and  finally  opens  to  the  exterior  by  funnel-shaped  oscula  (os.,  Fig.  34)  at 
the  tips  of  the  numerous  ultimate  branches,  and  at  many  places  along  the  course  of  the 
tube.  The  margins  of  these  oscula,  or  oral  funnels,  are  provided  with  short  tentacle-like 
projections,  the  digitella.  These  are  covered  by  an  epithelium  containing  nettle  cells, 
and  each  has  a  gelatinous  axis  in  which  there  are  transverse  plates  of  greater  density 
than  the  rest  of  the  jelly,  and  these  give  the  structure  the  cellular  appearance  first 
described  by  Hamann  ('8l) .  The  epithelium  lining  the  tubes  and  funnels  is 
ciliated. 

There  open  also  into  the  brachial  canals  the  lumina  of  the  oral  vesicles  (v.,  Fig.  34) . 
These  structures,  as  already  stated  in  the  diagnosis,  have  their  points  of  attachment  in 
the  axils  of  the  branches.  All  except  the  smallest  are  flattened  laterally.  The  smaller 
ones  are  oval  in  outline,  the  larger  ones  linear.  At  one  side  near  the  apex  there  is  a 
cluster  of  short  processes  that  Hamann  has  homologized  with  digitella. 

The  Oral  Disc.  —  Although  the  eight  oral  arms  seem  to  be  placed  at  equal 
distances  and  to  be  alike,  they  are  morphologically  in  pairs,  each  pair  being  homologous 
to  one  of  the  four  lips  of  a  semostomous  medusa,  —  an  aurelia,  for  example.  The  line 
that  separates  two  members  of  a  pair  is  therefore,  according  to  Haeckel's  nomenclature 
a  perradius.  The  brachial  canals  from  each  pair  of  arms,  on  entering  the  oral  disc, 
converge  and  unite  into  a  single  radial  tube  that  is  continued  to  the  centre  of  the  disc, 
where  it  unites  with  the  other  three.  In  this  way  the  course  of  the  tubes  on  the  oral 
disc  forms  a  pattern  that  resembles  a  Maltese  cross.  The  larger  central  vesicle  is 
attached  at  the  centre  of  the  cross.  In  a  living  specimen  11  cm.  in  diameter  this 
measured  3  cm.  in  length.  There  are  four  other  vesicles  that  most  nearly  approach  the 
central  one  in  size,  and  these  arise  from  the  radial  canals  near  the  junction  of  the 
brachial  canals,  and  I  have  called  them,  therefore,  the  radial  vesicles.  In  full-grown 
individuals  there  are  eight  more  vesicles  upon  the  oral  disc,  a  little  smaller  than  the  last, 
one  on  each  brachial  canal  distal  to  the  junction.  It  is  only  near  the  periphery  of  the 


CASSIOPEA   XAMACHANA.  205 

disc  that  the  canals  are  provided  with  oral  funnels.  For  most  of  their  course  on  the  disc 
the  canals  give  rise  to  the  very  small  vesicles,  finely  speckled  with  a  reddish  brown 
pigment,  that  already  have  been  mentioned.  These  have  nettle  batteries  at  their  tips, 
and  are  so  numerous  as  to  cover  completely  the  greater  part  of  the  disc  and  to  hide  the 
course  of  the  canals.  This  mass  of  small  vesicles,  however,  is  not  acquired  until  late. 
Specimens  as  much  as  6  cm.  in  diameter  will  be  found  to  be  without  them.  In  such 
specimens  we  have  the  five  largest  vesicles,  and  a  number  of  oral  funnels  are  scattered 
along  the  canals,  just  as  they  are  upon  the  arms.  This  replacement  of  the  oscula  on  the 
oral  disc  by  small  vesicles  has  been  observed  to  occur  also  on  adult  females  of  Polyclonia 
frondosa,  but  not  in  the  males  (Bigelow,  '93) .  It  is  not  improbable  therefore  that  a 
similar  difference  between  the  sexes  may  be  discovered  in  our  species  of  Cassiopea. 

The  Subgenital  Cavities  and  the  Digestive  Tract.  —  At  each  of  the  four  points 
of  junction  of  the  brachial  canals  there  is  a  slit-like  passage,  oesophageal  canal,  dipping 
vertically  into  the  mesogloea  of  the  disc,  and  opening  into  the  stomach.  The  latter  is 
a  lens-shaped  cavity,  with  a  gently  arched  roof.  Its  floor  consists  chiefly  of  four  lozenge- 
shaped  areas,  where  the  body  wall  is  very  thin  and  plaited  in  radial  folds  (Fig.  34) . 
These  thin  parts  of  the  'body  wall  form  the  roofs  of  the  subgenital  cavities,  which  open 
to  the  exterior,  each  by  an  elliptical  orifice,  osteum,  (x,  Fig.  34)  in  the  side  of  the  oral 
disc  near  the  subumbrella  and  in  the  angle  between  two  pairs  of  arms  (interradial) . 
The  gonad  appears  as  a  band  which  crosses  this  membrane  tangentially  at  its  greatest 
width.  Just  central  to  each  gonad  there  is  a  multiple  series  of  very  many  small  gas- 
tric filaments  forming  a  narrow  band  parallel  to  the  ovary.  These  are  ciliated,  and 
provided  with  nettle  and  gland  cells.  The  portion  of  the  floor  of  the  stomach  not  made 
up  of  these  lozenge-shaped  membranes  is  bounded  by  the  firm  mesogloea  of  the  oral  disc. 
This  area  has  the  shape  of  a  Maltese  cross,  and  it  is  in  the  arms  of  this  cross,  between  the 
subgenital  cavities,  that  the  passages  from  the  oral  canals  open  into  the  stomach. 

Near  its  periphery  the  floor  of  the  stomach  is  marked  by  radial  grooves.  These  are 
continued,  each  into  one  of  the  radial  canals  that  extend  outward  from  the  edge  of  the 
circular  stomach  to  the  marginal  region  of  the  umbrella.  There  are  regularly  thirty-two 
of  these,  sixteen  in  the  radii  of  the  rhopalia,  and  sixteen  interrhopalial.  When  the 
number  of  rhopalia  is  increased,  the  number  of  radial  canals  may  or  may  not  increase  in 
proportion.  There  are  often  thirty-four  or  thirty-six  of  them.  The  canals  in  the 
radii  of  the  rhopalia  are  larger  and  more  nearly  straight  than  the  interrhopalial  ones,  and 
all  are  connected  by  a  fine  network  of  anastomosing  branches,  among  which  no  distinct 
circular  canal  can  be  recognized.  The  meshes  in  the  network  of  canals  are  connected  by  a 
plate  of  endodermal  cells,  the  endodermal  lamella.  This  lamella  is  also  in  contact  with  the 
subumbrellar  ectoderm  along  a  line  encircling  the  umbrella  a  short  distance  from  its  mar- 


206  ROBERT   PAYNE   BIGELOW    ON 

gin,  so  that  there  is  a  complete  sheet  of  endodenn  separating  the  subumbrellar  from  the 
exumbrellar  mesogloea. 

Musculature.  —  The  exumbrella  is  devoid  of  muscles,  but  on  the  opposite  side 
there  is  a  continuous  sheet  of  muscle  fibres,  which  is  spread  over  the  subumbrella, 
except  a  narrow  zone  at  its  margin,  and  is  continued  over  the  oral  arms  to  their  finest 
ramifications,  and  also  into  the  subgenital  cavities. 

Most  of  the  fibres  on  the  subumbrella  do  not  take  an  evenly  circular  course,  but  are 
undulating.  They  form  in  this  way  a  series  of  double  "  arcades  "  like  those  found  by 
Haeckel  in  other  species  of  Cassiopea.  There  is  one  of  these  double  arcades  for  each 
interrhopalial  space.  The  surface  of  the  mesogloea  in  this  region  is  grooved.  The 
sheet  of  muscle  fibres  lies  directly  upon  it,  and  is  therefore  corrugated,  the  grooves 
being  parallel  with  the  fibres. 

The  muscular  layer  upon  the  oral  arms  is  smooth,  and  its  fibres  take  a  longitudinal 
course,  extending  to  the  digitella  and  oral  vesicles. 

In  the  subgenital  cavities  the  arrangement  of  the  muscle  fibres  could  not  be  made 
out;  but  their  presence  was  revealed  by  the  squirming  movements  of  the  thin  membrane 
that  separates  the  subgenital  cavity  and  bears  the  gonads  and  gastric  filaments. 

Structure  of  the  Marginal  Sense  Organs.  —  Each  rhopalium  has  a  pigment  spot 
on  the  aboral  side  near  the  extremity,  and  each  one  lies  in  a  deep  sensory  niche.  The 
dorsal  sensory  groove,  common  in  the  Pelagidae,  Aurelia,  etc.,  is  entirely  lacking; 
although  Keller  found  in  C.  polypoides  a  slightly  depressed  thickening  of  the  ectoderm 
that  corresponds  to  it.  The  sensory  niche  and  rhopalium  are,  with  the  exception  of  the 
pigment  spot,  similar  in  all  essential  particulars  to  those  found  in  Pelagia.  The 
rhopalium  is  the  only  organ  in  the  sensory  niche  (Fig.  56).  It  is  a  hollow,  finger-like 
projection  attached  by  its  base  to  a  low  ridge  that  runs  along  the  roof  to  the  central  wall 
of  the  niche.  This  ridge  is  penetrated  longitudinally  by  the  continuation  of  a  radial 
canal  from  the  stomach,  and  the  lumen  of  the  rhopalium  opens  into  the  distal  end  of  this 
canal.  In  the  distal  half  of  the  rhopalium  the  lumen  is  nearly  obliterated  by  the  increase 
in  thickness  of  its  endodermal  lining.  Here  the  endoderm,  instead  of  being  a  columnar 
epithelium  as  elsewhere,  is  a  mass  of  parenchyma-like  cells,  each  of  which  contains  a 
large  calcareous  concretion,  a  so-called  otolith.  A  thin,  supporting  membrane  separates 
the  endoderm  from  the  ectoderm.  At  the  distal  extremity  of  the  rhopalium  the  ecto- 
derm is  a  thin,  cuboidal  epithelium,  while  over  the  rest  of  the  surface  it  is  a  thick,  sensory 
epithelium  resting  on  a  thick  network  of  fine  nerve  fibres.  This,  in  turn,  rests  on  the 
supporting  membrane.  I  have  observed  no  ganglion  cells  in  this  layer  of  nerve  fibres, 
which  is  continued  under  the  epithelium  of  the  rhopalial  ridge  to  the  central  wall  of  the 
niche,  where  it  becomes  imperceptible.  There  are  no  thickened  bands  of  these  fibres 


CASSIOPEA  XAMACHANA.  207 

running  to  ciliated  pockets,  such  as  are  found  in  Dactylometra  (Bigelow,  '90),  and  the 
fibres  probably  spread  out  finally  into  a  thin  network  underlying  the  general  epithelium 
of  the  subumbrella. 

The  one  feature  in  which  this  rhopaliurn  differs  from  what  is  found  in  Pelagia  is  the 
presence  of  the  pigment  spot,  already  mentioned,  lying  on  the  aboral  side  of  the 
rhopalium  immediately  above  the  centre  of  the  mass  of  concretions.  This  area  is 
probably  sensitive  to  light,  but  it  only  differs  from  the  rest  of  the  sensory  epithelium  in 
that  here  the  superficial  cells  are  deeply  colored  by  a  yellowish  brown  pigment.  A 
more  careful  examination  would  undoubtedly  show  the  histology  of  this  structure  to  be 
similar  to  what  Schewakoff  ('89)  has  found  in  Aurelia. 

HABITS. 

The  species  of  Cassiopea  and  the  closely  related  genus  Polyclonia  find  their  habitat 
usually  in  quiet  lagoons  among  the  mangroves  along  the  shores  of  the  tropical  seas.  The 
mode  of  life  of  several  species  has  been  described  by  Brandt  ('38)  on  the  authority  of 
Merten.s,  L.  Agassiz  ('62),  Gray  ('69),  A.  Agassiz  ('8l),  Archer  ('8l),Fewkes  ('82),  Guppy 
('82) ,  and  Agassiz  and  Mayer  ('99) .  Cassiopea  xamachana  is  no  exception  to  the  rule 
either  in  its  habitat  or  its  sedentary  mode  of  life. 

When  the  young  medusa  is  set  free  from  the  strobila  it  is  an  active  swimmer.  It 
gradually  becomes  less  active  as  the  mouth  parts  acquire  their  adult  structure,  and  by 
the  time  the  animal  has  reached  a  diameter  of  two  centimeters  it  has  definitely  taken 
up  its  abode  upon  the  bottom.  It  lies  there,  as  described  in  the  Introduction,  with  the 
oral  appendages  upward,  and  seldom  changes  its  position  unless  disturbed.  The  con- 
cavity of  the  exumbrella  is  an  important  aid  in  maintaining  this  posture  against  the 
action  of  waves  and  currents.  The  gelatinous  tissue  is  firm  and  elastic,  and  causes  the 
umbrella  to  assume  its  normal  shape  when  the  subumbrellar  muscles  are  relaxed.  The 
slight  suction  thus  produced  when  the  medusa  comes  to  rest  on  a  flat  surface  gives  it 
such  a  hold  that  a  certain  amount  of  force  is  required  to  remove  it. 

Usually,  however,  the  water  in  the  lagoons  is  very  quiet,  and  there  is  more  danger 
from  its  stagnation  than  from  its  motion.  A  Cassiopea  is  enabled  to  avert  this  danger  by 
the  slight  swimming  movements  of  the  thinner  marginal  part  of  the  umbrella.  By 
means  of  these  rhythmic  contractions  the  water  is  drawn  in  on  all  sides,  and  then  is 
driven  upward  and  away.  A  healthy  specimen  lying  undisturbed  on  the  bottom  of  an 
aquarium  was  observed  during  seven  minutes  to  make  on  the  average  19.7  contractions 
of  the  umbrella  per  minute.  In  this  way  the  animal  is  enabled  to  draw  to  itself  a  fresh 
supply  of  oxygen  and  of  its  minute  food  material. 


208  ROBERT  PAYNE  BIGELOW   ON 

The  oral  arras  and  their  branches  are  usually  spread  out  so  as  to  cover  the  sub- 
umbrella  completely,  but  they  are  almost  always  in  motion,  bending  to  one  side  or  the 
other,  and  they  may  be  flexed  aborally  until  the  tips  come  within  the  umbrellar 
margin,  or  extended  until  they  reach  far  beyond.  Besides  these  general  movements, 
the  various  appendages  of  the  oral  arms  have  movements  of  their  own.  Muscular  con- 
tractions may  be  observed  also  in  the  thin  membrane  that  separates  the  stomach  from 
the  subgenital  cavities,  and  they  probably  serve  to  renew  the  water  that  bathes  the 
gonads. 

When  the  oral  disc  has  been  severed  from  the  umbrella,  both  parts  may  remain 
alive  for  several  days,  and  both  retain  their  powers  of  spontaneous  movement.  The  first 
effect  of  the  operation  is  often  to  throw  all  of  the  parts  into  a  strong  tetanus,  but  shortly 
afterwards  the  pulsations  of  the  umbrella  may  be  renewed  at  a  rate  considerably  more 
rapid  than  normal,  —  32  to  34  per  minute  in  one  case.  When  the  medusae  have  been 
for  some  time  under  unfavorable  conditions,  it  frequently  happens  that  the  part  of  the 
body-wall  surrounding  the  periphery  of  the  stomach  is  ruptured,  and  thus  the  mouth  parts 
as  a  whole  become  separated  automatically  from  the  umbrella.1 

While  at  Bimini,  Bahamas,  in  1892,  I  observed  that  the  food  of  Polyclonia  f rondo sa 
consists  chiefly  of  copepods  and  other  small  Crustacea,  and  that  these  are  caught  by  the 
combined  action  of  the  oral  vesicles  and  the  oscula  ('93,  p.  106).  If  a  copepod  strikes 
a  vesicle,  the  vesicle  bends  quickly  so  as  to  cover  the  mouth  of  the  adjoining  oscu- 
lum,  and  the  copepod  is  thus  enclosed  in  a  trap.  Artificial  stimulation  would  cause  the 
same  reaction. 

Experiments  on  Cassiopea  xamachana  made  to  determine  whether  or  not  this 
species  obtains  its  food  in  the  same  way  gave  negative  results.  Stimulation  of  an  oral 
vesicle  causes  only  a  slight  bending  on  the  side  stimulated.  Although  these  vesicles  are 
provided  with  batteries  of  nettle  cells  near  the  tip,  I  was  unable  to  see  that  they  played 
any  part  in  the  taking  of  food.  It  may  be  that  they  are  protective,  but  the  sting  is 
very  feeble. 

Examinations  of  the  contents  of  the  stomach  were  almost  equally  unsatisfactory. 
The  contents  of  twenty-two  stomachs  were  examined,  and  of  these  fourteen  contained 
only  a  clear,  very  viscous  fluid  and,  in  some  cases,  a  few  apparently  ripe  eggs,  more  or 
less  distorted,  some  small,  colorless  cells,  probably  sloughed  off  from  the  endodermal 
epithelium,  and  green  cells  identical  with  the  "  zoanthelae  ''  found  in  the  mesogloea.  One 
or  more  copepods  and  other  Crustacea  were  found  in  five  specimens.  In  one  of  these  one 
small  amphipod  was  found,  and  in  another  the  cornea  of  an  unknown  crustacean. 

1  While^this  paper  is  passing  through  the  press  a  paper  has  appeared  by  E.  W.  Berger  (1900),  in  which  lie  gives  the 
results  of  experiments  made  by  F.  S.  Conant  upon  Polyelonia  and  Cassiopea  to  test  the  effect  of  removing  the  rhopalia. 


CASSIOPEA  XAMACHANA.  209 

Diatoms  and  other  algae,  exclusive  of  the  above-mentioned  zoanthelae,  were  found 
in  four  cases  out  of  the  twenty-two.  Almost  always  the  first  impression  on  opening  a 
stomach  was  that  it  was  empty;  and  it  was  only  by  careful  examination  that  the  contents 
of  the  stomach  could  be  discovered.  In  two  cases,  however,  a  considerable  amount 
of  material  was  found  in  the  stomach.  In  one  of  these  the  stomach  contained,  besides 
the  usual  eggs,  zoanthelae,  debris,  etc.,  the  remains  of  many  copepods,  some  nematods, 
a  zoea,  and  some  diatoms.  In  the  other  one  there  was  found  a  compact  greenish  mass, 
about  one  centimeter  in  diameter,  composed  of  granular  debris  and  diatoms  of  various 
species,  together  with  some  desmids,  Oscillaria,  foraminifera,  infusoria,  Vorticella,  and 
some  fine  filaments  with  spirally  arranged  contents. 

This  species  exhibits  the  power  of  regeneration  of  lost  parts  to  a  marked  extent. 
Specimens  were  frequently  met  with  in  which  branches  of  the  oral  arms,  or  even  portions 
of  the  margin  of  the  umbrella,  had  evidently  been  formed  recently  to  replace  parts  that 
had  been  destroyed.  Moreover,  branches  of  the  oral  arms  that  had  been  cut  off  were 
observed  to  regenerate  oscula  and  vesicles  at  the  central  end. 


ONTOGENY. 

Historical  Review.  —  Numerous  studies  upon  the  reproduction  of  various  animals 
by  budding  have  shown  that  the  formation  of  organs  in  the  bud  may  take  an  entirely 
different  course  from  the  development  of  homologous  organs  in  the  sexually  produced 
embryo.  As  the  observations  to  be  described  in  the  sequel  were  made  entirely  upon 
larvae  that  were  observed,  or  supposed,  to  be  asexually  produced,  they  cannot  settle 
any  of  the  disputed  points  in  regard  to  the  development  of  sexually  produced  larvae. 
Nevertheless  it  will  be  of  interest  to  compare  the  sexual  with  the  asexual  mode  of 
ontogeny,  especially  as  the  development  of  a  scyphistoma  from  a  bud  has  never  before 
been  fully  described. 

The  development  of  scyphomedusae  from  the  egg  has  been  studied  in  comparatively 
few  forms.  Several  species  of  Aurelia  have  been  studied  by  Sars,  Haeckel,  Schneider, 
Glaus,  Goette,  Frank  Smith,  and  Hyde.  Two  species  of  Cyanea  have  been  studied  by 
McMurrich  and  Hyde.  A  species  of  Chrysaora  has  been  studied  by  Glaus;  and 
Kowalewsky,  Metschnikoff,  Krohn,  and  Goette  have  traced  the  very  interesting  abbrevi- 
ated development  of  Pelagia  noctiluca.  The  nearest  ally  of  our  species  that  has  been 
studied  with  any  degree  of  completeness  is  the  Mediterranean  rhyzostome  Cotylorhiza 
tuberculata,  which  has  been  the  subject  of  investigation  by  Glaus  and  Goette. 

From  the  description  of  the  process  of  budding  given  in  the- next  section,  it  will  be 


210 


ROBERT  PAYNE   BIGELOW   ON 


d- 


—  d 


noted  that  the  larvae  produced  by  budding  are  set  free  in  a  form  resembling  planulae, 

and  it   is  the   planula  stage  in  sexual    reproduction  which  is  the  earliest  that  can  be 

compared  with  any  stage  to  be  described  in  this  paper. 

All   agree  that  the  planula  of  the  Scyphomedusae  is  a  more  or  less  oval,  ciliated 

larva,  somewhat  flattened  on  one  side.     It  consists  of  two  layers  of  cells  surrounding  a 

cavity  which  is  completely  shut  off  from 
the  exterior.  The  first  step  toward  the 
development  of  the  scyphistoma  is  an  in- 
vagination  of  the  ectoderm  at  the  posterior 
pole  of  the  planula.  According  to  Goette 
and  Miss  Hyde,  the  endoderm  is  invagina- 
ted  at  the  same  time  in  such  a  way  that 
two  endodermal  pouches  remain  in  the 
plane  of  the  long  diameter, —  "Haupte- 
bene,"  Goette, —  (Pig.  B,  and  b-b  Fig. 
D),  one  on  each  side  of  the  invagination, 
while  the  endoderm  is  pushed  entirely 
away  from  the  oral  pole  in  the  plane  of 
the  short  diameter  (Fig.  C,  and  c-c  Fig. 
D) .  The  ectodermal  invagination  is  the 
oesophagus  (Schlund) ,  its  external  open- 
ing is  the  mouth,  and  the  endodermal 
evaginations  are  the  first  pair  of  gastric 
pouches.  Soon  an  opening  is  formed 
(Schlundpforte)  between  the  base  of  the 
oesophagus  and  the  central  stomach,  and 
at  the  edge  of  the  opening  the  ectoderm 
fuses  with  the  endoderm.  Then  the  sec- 
ond pair  of  gastric  pouches  is  formed. 
According  to  Goette  these  are  produced  in 
Cotylorhiza  and  Pelagia  entirely  from  the 


g— 


Figs.  B-G.  Two  stages  in  the  development  of  the  mouth 
and  gastric  pouches  in  a  sexually  produced  scyphistoma, 
according  to  Goette.  Figs.  B  to  I)  are  sections  in  the  three 
dimensions  of  space  of  a  larva  in  which  the  oesophagus  is 
invaginated  and  the  first  pair  of  gastric  pouches  are  formed. 
Figs.  E  to  G  are  similar  sections  of  a  larva  in  which  the  open- 
ing from  the  oesophagus  into  the  stomach  (Schlundpforte)  has 
been  established  and  the  second  pair  of  gastric  pouches  are  in 
the  process  of  formation.  6,  c,  d,  etc.,  indicate  the  plane  of 
Figs.  B,  C,  D,  etc. 

opening  (Schlundpforte) ,  and  are  therefore 
at  the  level  of  the  upper  edges  of  the  first  pair  of  pouches.     As  these  pouches  extend  out- 


ectoderm  of  the  lower  part  of  the  oesopha- 
gus (Fig.  F) .     According  to  his  view  the 
lower  edges  of  these  evaginations  coincide  . 
with  the  margin  of  the  gastro-oesophageal 


CASSIOPEA   XAMACIIANA.  211 

ward  the  ectoderm  is  pushed  out  until  the  principal  radii)  e-e  and  f-f,  Fig.  G)  gradually 
become'  equal.  This  results  in  the  formation  of  the  flattened  peristomal  disc  (Figs.  E 
and  F) .  At  the  same  time  the  wall  separating  the  oesophagus  from  the  first  pair  of  gastric 
pouches  (Taschenvorhang)  is  split  upward  until  the  openings  into  the  two  pairs  of  pouches 
are  upon  the  same  level,  and  the  "  Taschenvorhang  "  is  reduced  to  a  low  ridge,  while  the 
oesophagus  is  very  much  shortened.  Portions  of  the  original  lining  of  the  lower  part  of 
the  oesophagus  persist  as  the  covering  of  the  inner  edges  of  the  septa  which  separate  the 
four  gastric  pouches.  The  larva  is  now  in  what  Goette  calls  the  scyphula  stage.  He 
regards  this  stage  as  of  great  phylogenetic  importance,  showing  clearly,  he  thinks,  a 
close  genetic  connection  between  the  Scyphomedusae  and  the  Anthozoa ;  so  that  these 
groups  should  be  placed  in  a  single  class,  Scyphozoa,  to  distinguish  them,  on  the  one 
hand,  from  the  Hydrozoa,  including  the  hydroids,  hydromedusae,  and,  on  the  other,  from 
the  Siphonophorae. 

This  view,  which  is  confirmed  by  Miss  Hyde,  is  antagonized  by  Glaus,  and  has  given 
rise  to  a  prolonged  controversy.  The  parties  to  this  dispute  are  practically  in  accord 
in  regard  to  the  facts  of  observation,  as  represented  by  the  figures  in  their  latest 
contributions.  It  is  in  the  interpretation  of  these  facts  that  they  differ  mainly.  Glaus 
('90)  admits  that  there  is  an  ectodermal  invagination  previous  to  the  formation  of  the 
mouth,  and  that  the  lining  of  the  proboscis  is  ectodermal.  He  maintains,  however,  that 
the  condition  represented  in  Figs.  B,  C,  and  D,  is  due  to  a  severe  contraction  of  the 
animal,  and  is  without  morphological  significance.  He  denies  that  there  is  any 
oesophagus,  "  Taschenvorhang,"  or  "  Schlundpforte,"  in  the  sense  that  Goette  uses  these 
terms  ;  and  with  these  he  rejects  the  idea  of  a  close  affinity  between  the  Anthozoa  and 
scyphomedusae,  with  the  correspondingly  sharp  distinction  between  the  latter  and  the 
hydromedusae.  He  admits,  however,  that  a  distinction  of  importance  between  scyphis- 
torna  and  hydropolyp  is  to  be  found  in  the  possession  by  the  former  of  an  ectodermal 
lining  of  the  proboscis,  and  in  the  presence  of  gastric  pouches  and  septa. 

Goette's  position  has  been  strengthened  considerably  by  his  latest  contribution  on 
this  subject  ('93),  and  his  conclusions  are  confirmed  in  nearly  every  particular  by  Miss 
Hyde.  Goette's  figures  appear  to  be  camera  drawings  of  serial  sections,  and  are  a 
great  improvement  over  the  rather  diagrammatic  illustrations  in  his  earlier  papers. 
They  are  not  entirely  convincing,  however,  for  the  ectoderm  and  the  endoderm  grade 
into  each  other  so  that  it  is  impossible  to  determine  the  exact  boundary ;  and  the 
material  is  so  subject  to  distortion  during  the  preservation  that  it  is  often  difficult  to 
determine  whether  a  given  fold  of  the  epithelium  is  of  morphological  value  or  is  merely 
an  artifact. 

Miss  Hyde  fails  to  confirm  the  view  that  the  whole  of  the  second  pair  of  gastric 


212  ROBERT   PAYNE   BIGELOW   ON 

pouches  (and  hence,  according  to  Goette,  five  eighths  of  the  peripheral  digestive  tract  of 
the  medusa)  is  of  ectodermal  origin.  On  page  550  of  her  paper  she  speaks  of  only  the 
roof,  i.  e.,  the  lining  of  the  oral  side,  of  these  pouches  as  formed  from  oesophageal  ecto- 
derm, and  her  sections  bear  out  this  view. 

The  foregoing  brief  summary  of  the  present  state  of  knowledge  regarding  the  early 
stages  in  the  development  of  the  sexually  produced  scyphistoma  will  serve  as  an 
introduction  to  what  is  to  follow.  Mention  of  the  work  of  others  upon  the  later  stages 
will  be  made  when  we  come  to  the  corresponding  periods  in  the  development  of 
Cassiopea  xamachana. 

The  Formation  of  the  Bud.  —  In  1841  Sars  described  the  budding  of  scyphistomas 
that  were  supposed  to  belong  to  a  species  of  either  Aurelia  or  Cyanea.  The  buds,  accord- 
ing to  this  account,  may  grow  out  directly  from  the  main  part  of  the  body  of  the  larva, 
or  they  may  be  produced  on  stolons  extending  outward  from  the  foot.  In  either  case, 
several  buds  may  be  formed,  apparently  in  various  positions  on  the  scyphistoma  at  one 
time.  The  figures  show  the  buds  attached  to  the  parent  and  provided  with  a  well- 
developed  crown  of  tentacles  at  the  distal  end.  Agassiz  ('60)  found  a  similar  process  of 
budding  to  occur  occasionally  in  Aurelia.  Goette  ('87)  has  confirmed  these  observations, 
and  has  found  that  the  larvae  of  Cotylorhiza  tubereulata  also  produce  buds. 

In  Cotylorhiza  the  bud  is  formed  as  an  outgrowth  from  the  body  of  the  scyphistoma ; 
and  as  it  grows  it  gradually  approaches  the  shape  of  its  parent,  but  its  relative  position  is 
just  the  reverse  of  what  Sars  found ;  for  the  distal  end  forms  the  stem,  and  the  proximal 
end  begins  to  flatten  out  into  a  circumoral  disc.  In  this  condition  the  bud  is  set  free,  and 
swims  about,  rotating  on  its  long  axis,  with  its  distal  end  forward.  The  mouth  is  formed 
at  the  point  where  the  constriction  finally  separates  the  bud  from  its  parent,  and  the  larva 
fixes  itself  by  the  opposite  end. 

Glaus  ('92)  has  found  that  the  scyphistomas  of  Cotylorhiza  not  only  produce  buds, 
but  that  they  produce  them  in  large  numbers.  Scyphistomas  reared  from  eggs  that  had 
been  laid  in  September,  1890,  were  kept  alive  in  the  aquaria  at  Trieste  and  Vienna 
throughout  the  following  winter  and  spring.  No  change  was  observed  after  the  larvae 
had  reached  the  sixteen-tentacle  stage,  until  the  following  July,  when  budding  occurred. 
The  process  was  not  restricted  to  a  few  well-nourished  individuals,  but  seemed  to  be  a  gen- 
eral and  repeated  phenomenon,  and  it  resulted  in  a  large  increase  in  the  number  of  larvae. 
Claus's  brief  description  of  the  formation  and  fate  of  the  bud,  accompanied  by  three 
figures,  corresponds  perfectly  with  what  I  have  to  describe  in  the  following  pages.  The 
strobilization,  he  says,  took  place  in  August,  and  was  monodiscous. 

Another  case  of  rapid  multiplication  of  scyphistomas  by  budding  is  described  by 
Lacaze-Duthiers  ('93) .  A  colony  of  these  larvae,  of  unknown  origin,  was  discovered  in 


CASSIOPEA   XAMACHANA.  213 

an  aquarium  at  Banyuls  in  1892.  No  strobila  or  ephyra  was  observed  up  to  October, 
1893,  but  in  the  meantime  the  number  of  scyphistomas  had  increased  enormously.  The 
buds  appeared  as  elevations  on  the  side  of  large  individuals.  The  base  of  this  elevation 
became  elongated  into  a  filamentous  stolon  carrying  the  bud  at  its  tip.  The  bud  fixed 
itself  to  the  glass,  gradually  developed  tentacles,  and  finally  became  independent  by  the 
disappearance  of  the  stolon. 

In  Cassiopea  xamachana  the  process  of  budding  is  an  important,  if  not  the  chief,  factor 
in  the  perpetuation  of  the  species.  On  looking  over  collections  of  scyphistomas  taken 
from  the  Great  Salt  Pond  during  May,  June,  and  July,  a  considerable  number  was  found 
with  buds  attached  in  various  stages  of  development  (Figs.  1,  2,  and  26),  and  budding 
continued  in  the  aquaria. 

There  is  no  stolon.  The  first  visible  rudiment  of  the  bud  is  a  slight  swelling  on  one 
side  of  the  calyx  just  above  where  it  tapers  into  the  stem.  It  involves  all  three  layers  of 
the  body  wall  (Fig.  36) .  At  an  early  stage  in  the  growth  of  the  bud  the  four  septal 
muscles  may  be  found  as  four  slender  cords  of  cells  embedded  in  the  mesogloea  and  appar- 
ently growing  out  from  a  thickened  area  of  the  ectoderm  at  the  apex  of  the  bud  (sm, 
Figs.  38  and  39) .  This  appearance  seems  to  indicate  that  the  septal  muscles  of  the  bud 
are  formed,  as  in  sexually  produced  scyphistomas,  by  an  ingrowth  of  the  ectoderm. 

Careful  study  of  serial  sections  through  young  buds  shows,  however,  that  the 
septal  muscles  of  the  bud  are  connected  with  septal  muscles  of  the  parent.  In 
Fig.  37  the  course  of  the  septal  muscles  is  reconstructed  from  a  series  of  longi- 
tudinal sections.  The  muscle  smt  passes  around  the  base  of  the  bud  on  the  side 
away  from  the  observer  and  gives  rise  to  two  branches,  sm\  and  sm'3.  These  extend 
toward  the  apex  of  the  bud,  and  each  one  divides  dichotymously.  Muscle  sm4  gives 
off  a  branch  which  fuses  with  sm^  at  the  base  of  the  bud.  Sm2  produces  three  branches 
which  unite  into  a  single  branch.  This  branch  extends  into  the  base  of  the  bud,  but  it 
was  impossible  to  trace  it  further.  It  may  be  connected,  perhaps,  with  the  muscle  sm'2, 
which  was  traced  for  a  short  distance  from  the  apex  of  the  bud. 

On  account  of  the  presence  of  the  muscles,  it  is  possible  to  study  the  relation  of  the 
plan  of  symmetry  of  even  young  buds  with  the  symmetry  of  the  parent.  A  series  of 
sections  made  at  right  angles  to  the  long  axis  of  the  bud  shows  that  the  vertical  perradii 
of  the  bud  lie  in  the  plane  of  one  of  the  perradii  of  the  parent.  But  in  transverse 
sections  it  is  impossible  to  trace  the  muscles  of  the  bud,  except  for  short  distances, 
owing  to  their  extreme  fineness.1 

However,  the  study  of  longitudinal  sections  makes  it  reasonably  certain  that  the  sep- 

1  The  position  of  the  bud  is  always  perradial,  although  in  some  preparations  it  appears  to  be  interradial,  owing  to  the 
obliquity  of  the  sections,  as  in  Fig.  36, 


214  ROBERT    PAYNE    BIGELOW    ON 

tal  muscles  of  the  bud  are  derived  from  outgnnvths  of  one  or  both  of  the  septal  muscles  of 
the  parent  which  lie  in  the  interradii  adjoining  the  perradial  area  of  bud  formation.  If  this 
be  true,  then  every  part  of  the  young  bud  is  formed  from  the  corresponding  part  of  the 
parent,  viz.,  —  ectoderm  from  ectoderm,  mesogloea  from  mesogloea,  endoderm  from  endo- 
derm,  muscles  from  muscles,  and  digestive  tract  from  digestive  tract.  There  is  no  indica- 
tion of  any  method  of  budding  of  the  kind  described  by  Lang  ('92) . 

In  the  young  bud  the  mesogloea  is  very  thin,  so  that  the  ectoderm  and  endoderm  are 
very  nearly  in  contact.  The  evagination  gradually  increases  in  size,  becoming  first  hemi- 
spherical and  then  more  elongated.  At  the  same  time  a  constriction  appears  close  to  the 
body  of  the  scyphistoma,  which  deepens  until  the  bud  becomes  a  spindle-shaped  body 
attached  to  its  parent  by  a  short  and  narrow  stem  consisting  of  a  film  of  mesogloea 
covered  with  ectoderm,  the  digestive  cavity  of  the  bud  being  entirely  closed  (Fig.  1) . 

Scyphistomas  are  never  found  with  more  than  two  buds  attached.  When  two  bvids 
are  present  they  are  always  of  different  ages,  and  the  elder  is  always  attached  to  the 
apex  of  the  younger  (Fig.  2) . 

The  Planula-like  Larva.  —  When  finally  constricted  off,  the  bud  is  a  simple,  spindle- 
shaped,  hollow  body,  without  trace  of  mouth  or  tentacles.  It  is  like  a  planula  in  form  and 
habits.  The  whole  surface  is  covered  with  cilia,  and  it  swims  about,-  rotating  from  right 
to  left  upon  its  long  axis.  In  swimming,  the  distal  end  is  directed  forward.  While  swim- 
ming, the  larva  is  constantly  changing  its  shape,  assuming  in  a  few  minutes  various  forms 
from  an  elongated  spindle  to  a  short  heart-shape  (Fig.  3,  A,  B  and  (7) .  It  swims  near 
the  bottom,  hiding  under  any  object  that  it  may  find  there.  When  it  strikes  an 
obstacle,  it  may  rest  there  quietly,  or  it  may  rotate  slowly  upon  its  long  axis.  In  all 
its  movements  it  reminds  one  very  strongly  of  Agassiz's  description  of  the  planulae 
of  Aurelia. 

The  larva  is  white,  speckled  with  a  few  greenish  brown  spots.  It  is  rather  opaque, 
but  much  of  the  structure  may  be  seen  in  a  living  specimen.  A  longitudinal  section  shows 
that  the  ectoderm  consists  of  a  deep  layer  of  very  narrow  and  clos.ely-packed  columnar 
cells  (Fig.  39) .  The  mesogloea  contains  a  few  green  cells  (producing  the  greenish  brown 
spots),  and  some  widely  scattered  colloblasts.  The  layer  is  thickest  at  the  equator, 
diminishing  gradually  to  a  very  thin  layer  at  both  ends.  The  four  septal  muscles  (am) 
are  seen  clearly  at  the  distal  end  of  the  larva,  embedded  in  the  mesogloea  and  united  with 
the  ectoderm  near  the  apex  (Fig.  38) .  In  one  specimen,  not  yet  detached  from  the 
parent,  it  was  possible  to  trace  one  of  the  muscles  all  the  way  from  the  proximal  to  the 
distal  end.  The  muscle  fibres  are  already  differentiated  and  line  the  tube  of  mesogloea, 
while  the  nuclei  occupy  a  central  position. 

The  endoderm  is  a  columnar  epithelium,  rather  thin,  with  the  cells  closely  packed 


CASSIOPEA  XAMACHANA.  215 

together  and  coarsely  granular  at  the  proximal  or  posterior  end  of  the  larva.  Toward 
the  equator  the  cells  become  higher ;  and  at  the  distal,  or  anterior,  end  they  are  large  and 
clear.  The  character  of  the  endoderm  makes  it  possible  to  identify  the  anterior  end  of 
the  swimming  larva  with  the  distal  end  of  the  bud. 

The  Formation  of  the  Mouth.  —  The  first  change  to  be  seen  in  the  swimming  larva 
is  the  formation  of  the  mouth,  which  occurs  two  or  three  days  after  the  larva  has  been  set 
free.  When  writing  my  preliminary  paper  ('92  a) ,  I  was  in  doubt  as  to  the  relation 
between  the  poles  of  the  bud  and  those  of  the  larva.  The  better  and  more  abundant 
material  obtained  during  the  second  visit  to  Jamaica  proved  conclusively  that  the  proxi- 
mal end  of  the  bud  forms  the  oral  end  of  the  larva,  just  as  it  does  in  Cotylorhiza,  accord- 
ing to  Goette.  The  identification  is  made  easy  by  the  polar  differentiation  of  the 
endoderm  described  in  the  previous  section. 

When  first  seen  the  mouth  looks  like  a  minute  pin-hole  in  the  posterior  end  of  the 
larva  (m,  Fig.  4  B) .  In  longitudinal  sections  at  this  stage  the  first  indication  of  the  for- 
mation of  the  mouth  is  the  disappearance  of  the  mesogloea  from  a  small  area  at  the  poste- 
rior end,  so  that  there  is  no  longer  a  distinct  boundary  there  between  the  ectoderm  and 
endoderm  (m,  Fig.  40) .  At  the  same  time  a  small  dent  appears  in  the  outer  surface. 
This  deepens  until  it  forms  a  minute  tube  connecting  the  endodermal  cavity  with  the 
exterior  (Fig.  41) .  The  mouth  thus  formed  gradually  widens  and  becomes  slightly 
funnel-shaped. 

Further  stages  in  the  development  of  the  mouth  are  represented  in  Figs.  5,  6,  7.  In 
In  Fig.  6  there  is  a  distinct  circular  groove  which  outlines  the  base  of  the  proboscis  and 
separates  it  from  a  rudimentary  peristome.  In  Fig.  7  the  peristome  is  well  developed, 
and  the  mouth  is  widely  open. 

There  is  no  invagination  of  the  ectoderm  connected  with  the  formation  of  the  mouth, 
and  there  is  no  oesophagus,  "  Schlundpforte "  or  "  Taschenvorhang."  So,  if  Goette's 
account  of  the  formation  of  the  mouth  in  the  sexually  produced  scyphistomas  be  accepted, 
we  have  here  a  case  where  an  agamogenetic  differs  to  a  marked  degree  from  the 
gamogenetic  course  of  development. 

The  Scyphistoma.  —  With  the  elongation  of  the  forward  end,  the  formation  of  ten- 
tacles, and  the  development  of  four  gastric  pouches,  the  free-swimming  larva  becomes  a 
typical  scyphistoma. 

By  the  end  of  the  third  or  fourth  day  after  the  bud  has  been  set  free,  the  forward 
end  of  the  larva  has  elongated  to  form  a  stem  equal  in  length  to  the  rest  of  the  body 
(Figs.  7,  8,,  9,  and  11) .  The  end  of  the  stem  becomes  expanded,  generally  flattened,  and 
the  epithelium  covering  it  becomes  deeper  than  the  rest  (Fig.  42) .  This  epithelium  pro- 
duces a  secretion  which  serves  to  fasten  the  larva  to  some  solid  object.  Fixation  usually 
takes  place  during  the  fourth  or  fifth  day,  but  the  time  varies  greatly. 


216  ROBERT   PAYNE   BIGELOW   ON 

Development  of  the  Tentacles. —  During  the  third  day  the  peristome  appears  as  a  minute 
ridge  surrounding  the  posterior  end  of  the  larva,  a  short  distance  from  the  mouth.  The 
first  series  of  tentacles  arises  during  the  following  twenty-four  hours  as  four  perradial 
angles  in  the  margin  of  the  peristome  (Fig.  8) .  Four  interradial  tentacles  appear  almost 
simultaneously  with  these,  or  sometimes  considerably  later  (Figs.  9,  10,  11,  and  12) . 
The  elongation  of  the  tentacles  takes  place  rapidly,  so  that  at  about  the  end  of  the  sixth 
day  the  peristome  is  surmounted  by  a  crown  of  eight  tentacles,  which  equal  the  proboscis 
in  length. 

With  the  broadening  of  the  peristome  the  differentiation  of  the  body  of  the  scyphis- 
toma  into  stem  and  calyx  becomes  apparent  externally  (Figs.  13  and  14) .  When  the 
eight  perradial  and  interradial  tentacles  have  become  long  enough  to  reach  some  distance 
beyond  the  mouth,  eight  adradial  tentacles  appear  in  the  angles  between  them.  In 
Fig.  14  the  adradial  tentacles  are  distinctly  developed,  and  two  of  the  tentacles  of  the  first 
series  are  bifurcated  near  the  base.  Figs.  15  and  16  represent  the  typical  scyphistoma  in 
the  sixteen-tentacle  stage.  The  tentacles  are  now  long  and  graceful,  and  thickly  dotted 
with  batteries  of  nettle  cells. 

When  fully  developed,  the  scyphistoma  is  about  one  millimeter  and  a  half  in  diameter ; 
and  it  is  provided  typically  with  thirty-two  tentacles.1  But  there  is  as  much  variation  in 
the  number  of  tentacles  in  the  scyphistoma  as  there  is  in  the  number  of  sense  organs  and 
parameres  in  the  adult.  The  number  of  tentacles  is  seldom  less  than  thirty-two,  often 
greater.  The  way  in  which  this  variation  takes  place  is  indicated  in  Figs.  21  and  14. 
All  degrees  of  anomaly  maybe  observed, from  a  bifurcated  tentacle  shown  at  x  in  Fig.  21, 
through  the  condition  represented  in  Fig.  14,  to  two  completely  separated  tentacles  occu- 
pying the  position  of  one  typical  one. 

The  tentacles  of  a  well-developed  scyphistoma,  when  fully  expanded,  exceed  the 
length  of  the  body  several  times.  According  to  the  position  in  which  they  are  held,  the 
tentacles  may  be  divided  into  two  series.  Those  of  one  series  are  held  nearly  erect,  while 
those  of  the  other  series,  consisting  of  the  alternate  tentacles,  are  bent  backward  until 
their  tips  nearly  touch  the  ground  upon  which  the  animal  rests.  The  action  of  the  ten- 
tacles in  capturing  prey  may  be  observed  in  a  small  aquarium,  under  the  microscope.  As 
soon  as  a  tentacle  comes  into  contact  with  a  small  floating  body,  such  as  a  copepod,  it  is 
whipped  quickly  into  the  mouth,  and  at  the  same  instant  the  side  of  the  mouth  toward 
the  tentacle  is  opened  more  widely.  On  one  occasion  I  saw  two  tentacles  make  captures 
at  the  same  time,  and  the  mouth  expanded  in  both  directions  at  once,  showing  a  close 
co-ordination  between  the  movements  of  the  tentacles  and  of  the  mouth. 

1  Specimens  have  been  found  with  twenty-four  tentacles,  but  it  is  uncertain  whether  this  is  a  regular  stage  in  develop- 
ment between  the  sixteen-  and  thirty-two-tentacle  stage,  or  a  duplication  of  tentacles  of  the  earlier  stage. 


CASSIOPEA  XAMACHANA.  217 

Development  of  the  Gastric  Pouches. — While  the  final  result  is  the  same,  the  method 
of  development  of  the  gastric  pouches  differs  entirely  in  our  larva  from  the  process  as 
described  by  Goette.  The  free-swimming  larva  is  somewhat  flattened  laterally  (Fig.  4) , 
and  the  long  and  short  diameters  are  in  the  planes  of  the  perradii.  But  there  is  no 
evidence  that  the  gastric  pouches  in  the  long  diameter  are  formed  any  earlier  than  those  in 
the  short  diameter,  and  the  ectoderm  plays  no  part  in  their  development.  The  formation 
of  the  gastric  pouches  is  usually  described  as  a  process  of  evagination ;  but  in  this  case,  at 
least  in  the  earliest  stages,  the  delineation  of  the  pouches  seems  to  be  due  rather  to  the 
ingrowth  of  the  septa. 

These  appear  at  the  time  of  the  formation  of  the  first  tentacles  (Fig.  8)  as  four 
minute  vertical  folds  of  the  endoderm  (sep,  Fig.  43) ,  placed  equidistantly  in  the  angle 
formed  by  the  peristomal  fold  (compare  Fig.  42) .  The  mesogloeal  portion  of  the  septum 
is  at  first  very  thin,  and  in  the  four-tentacle  stage  (Figs.  8  and  43)  is  no  higher  than  the 
thickness  of  the  endodermal  layer  of  cells.  The  septal  muscles  do  not  penetrate  the  septa 
at  this  stage.  While  well-developed  below,  they  can  be  traced  upward  only  to  within 
35  or  41  p. *  from  the  base  of  the  septa. 

In  the  eight-tentacle  stage  (Fig.  13)  the  septum  is  still  very  small,  and  the  septal 
mesogloea  near  the  margin  of  the  peristome  is  very  thin,  hardly  thicker  than  a  cell  wall. 
But  at  the  central  margin  it  has  increased  in  thickness,  and  now  the  septal  muscle  may 
be  traced  from  the  stem  upward  through  this  thickened  portion  of  the  septal  mesogloea  to 
the  peristomal  ectoderm  (sm,  Figs.  44  and  47).  It  is  impossible  to  determine  whether 
the  new  portion  of  the  septal  muscles  is  formed  by  growth  upward  of  the  muscles  already 
present  in  the  stem,  or  whether  it  is  the  result  of  a  proliferation  of  the  peristomal  ecto- 
derm which  may  grow  downward  and  fuse  with  the  older  portion  of  the  septal  muscles. 

The  four  septa  are  now  complete,  and  divide  the  digestive  cavity  into  a  large 
central  stomach,  extending  into  the  stem,  and  four  shallow  marginal  gastric  pouches. 
The  gastric  pouches  expand  with  the  growth  of  the  peristomal  disc,  so  that  the  ecto- 
derm and  endoderm  remain  in  close  contact  at  the  margin ;  while  the  central  edges 
of  the  septa  retain  their  original  relative  position.  Thus  the  gastric  pouches  and  the  septa 
become  deeper  as  the  larva  increases  in  size.  This  is  evident  in  the  sixteen-tentacle  stage 
(Figs.  15  and  45  to  49) .  It  will  be  shown  later  that  the  relation  of  the  interradial  ten- 
tacles to  the  septa  is  variable.  In  this  stage,  however,  the  distal  part  of  the  septal  meso- 
gloea has  begun  to  disappear,  so  that  immediately  under  the  interradial  tentacles  the 
endoderm  of  adjacent  pouches  is  fused  (Figs.  45,  46,  and  47) .  In  the  fully  developed 
scyphistoma  this  area  of  fusion  is  perforated,  so  that  there  is  a  communication  between 
adjacent  pouches,  forming  the  "  Eingsinus "  of  German  authors.  In  the  specimen  with 

1  35  or  41  (i  =  about  one  seventh  of  the  length  of  the  larva. 


218  ROBERT   PAYNE   BIGELOW   ON 

forty-two  tentacles,  from  which  the  section  represented  in  Fig.  51  was  taken,  this  per- 
foration was  very  small.  Figs.  52  and  53  represent  a  little  later  stage,  in  which  the 
opening  has  become  much  wider. 

Each  septal  muscle  is  a  solid  cord  of  cells,  with  a  single  layer  of  longitudinal  muscle 
fibres  in  its  periphery.  In  the  peristome  the  fibres  of  the  septal  muscles  spread  out  in  a 
fan-shaped  arrangement  toward  the  margin. 

Four  slight  interradial  depressions  in  the  peristome  may  be  observed  as  early  as  the 
four-tentacle  stage.  They  are  deeper  in  the  eight-  and  sixteen-tentacle  stages,  and  the 
septal  muscles  may  be  seen  to  join  the  ectoderm  at  their  bottoms.  These  depressions  may 
be  homologous  with  the  septal  funnels  of  the  Stauromedusae,  or  they  may  be  merely  the 
result  of  the  contracted  condition  of  the  larva.  The  question  is  of  no  importance,  for 
there  can  be  no  doubt  about  the  homology  of  the  muscles ;  and  whether  they  are  solid  or 
hollow  is  merely  a  matter  of  detail.  In  later  stages  (Figs.  51  and  52)  sections  seem  to 
show  that  the  peristomal  depressions  have  deepened  centrally  so  as  to  leave  the  inser- 
tion of  the  septal  muscles  high  up  on  the  peripheral  side.  But  here,  again,  before  any 
morphological  conclusions  can  be  drawn,  account  must  be  taken  of  the  growth  of  the 
perradial  angles  of  the  proboscis  and  of  the  effect  of  the  contraction  of  the  septal  and 
peristomal  muscles. 

Relation  of  Septa  to  Interradial  Tentacles.  —  According  to  Goette,  the  interradial 
tentacles  are  always  interseptal  in  origin.  That  is,  two  of  these  tentacles  are  produced  as 
diverticulae  from  each  of  the  second  pair  of  gastric  pouches  (ectoderrnal) .  and  their  subse- 
quent position  in  the  planes  of  the  septa  is  due  to  a  secondary  shifting.  He  finds 
in  this  important  evidence  in  favor  of  his  theory  of  the  close  affinity  between  the 
Scyphomedusae  and  the  Anthozoa,  for  the  tentacles  of  the  latter  are  also  invariably  inter- 
septal. Glaus,  on  the  other  hand,  finds  that  the  interradial  tentacles  of  Aurelia  and  Coty- 
lorhiza  are  variable  in  origin.  According  to  his  observations  ('91  and  '92) ,  an  interradial 
tentacle  may  be  interseptal,  that  is,  arise  as  a  diverticulum  of  a  single  gastric  pouch,  the 
endoderm  growing  out  and  pushing  the  ectoderm  before  it ;  or  it  may  arise  in  the  plane  of 
a  septum  by  the  union  of  two  endodermal  diverticulae,  one  from  each  of  the  adjacent 
pouches.  He  holds,  therefore,  that  the  origin  of  the  tentacles  cannot  be  used  as  evidence 
to  uphold  Goette's  theory. 

My  observations  on  Cassiopea  are  in  perfect  accord  with  those  of  Glaus.  A  number 
of  series  of  transverse  serial  sections  made  from  young  scyphistomas  in  the  eight-  and 
sixteen-tentacle  stages  were  studied  carefully  with  the  aid  of  camera  sketches  drawn  on 
transparent  paper.  By  this  means  the  relations  of  the  parts  could  be  determined  accu- 
rately ;  and  the  results  are  embodied  in  the  series  of  diagrams,  Figs.  H  to  L.  In  the 
eight-tentacle  stage,  according  to  Goette,  the  gastric  pouches  in  the  long  diameter,  r  r, 


CASSIOPEA   XAMACHANA. 


219 


should  each  give  rise  to  a  single  tentacle,  while  the  pouches  in  the  short  diameter,  r'  r', 
should  each  produce  three.  From  a  glance  at  Figs.  H  and  J  it  will  be  seen  that  this  is 
not  the  case  in  Cassiopea.  To 

be  sure,  most  of  the  tentacles  at  J-J  I  J 

this  stage  are  interseptal  in 
position,  but  the  interradial  ten- 
tacles arise  as  often  from  pouch- 
es in  the  long  diameter,  r  r,  as 
from  those  in  the  short  diame- 
ter, r'  r' ;  and  in  both  Figs.  H 
and  I  there  is  one  interradial 
tentacle  that  is  distinctly  septal 
in  position.  The  septa  are  still 
complete,  so  that  there  can 
hardly  be  any  chance  of  a  shift- 
ing of  position.  In  the  sixteen- 
tentacle  stage,  there  is  a  ten- 
tacle in  the  plane  of  each  septum 
(Figs.  K  and  L)  ;  but  here  the 
perforation  of  the  septa  has 
commenced,  and  a  shifting  of 
relative  position  is  possible. 
Even  at  this  stage  irregularities  are  common.  For  example,  one  of  the  septa  in  Fig.  K  is 
placed  asymmetrically  with  relation  to  the  tentacles,  and  two  tentacles  are  wanting  in 
Fig.  L. 

The  Strobila,  —  Development  of  the  Rhopalia.  —  When  the  scyphistoma  has  reached  a 
diameter  of  about  two  millimeters,  there  appear  the  first  characters  that  are  distinctive  of 
the  strobila.  The  first  noticeable  change  in  this  direction  takes  place  at  the  bases  of  the 
tentacles  of  the  more  erect  series.  This  change  may  be  regarded  either  as  the  outgrowth  of 
a  conical  lobe  from  the  margin  of  the  circumoral  disc  bearing  the  tentacle  at  its  tip,  or  as 
a  conical  widening  of  the  basal  portion  of  the  tentacle.  The  former  view  is  probably  the 
better.  At  about  this  time  there  appear  in  the  tentacle,  just  beyond  the  apex  of  the  cone 
from  which  it  springs,  a  few  glistening  white  bodies.  These  are  the  so-called  otoliths,  and 
mark  the  beginning  of  the  formation  of  the  rhopalium  (Figs.  17  and  18).  The  tentacles 
containing  these  will  be  called  the  rhopalial  tentacles. 

These  concretions,  or  otoliths,  increase  in  number  until  they  form  a  conspic- 
uous mass,  while  the  basal  cone  begins  to  broaden  laterally.  This  is  now  distinctly  non- 


Figs.  H-L.  Diagrams  illustrating  the  space  relations  between  the  septa 
and  the  tentacles,  observed  in  five  young  scyphistomas  of  Cassiopea  xama- 
chana.  r  —  radii  of  the  long  diameter,  r'  —  radii  of  the  short  diameter. 


220  ROBERT   PAYNE   BIGELOW   ON 

contractile,  and  may  be  spoken  of  as  a  marginal  lobe  of  the  peristome  (Figs.  19  and 
20).  In  the  specimen  shown  in  Fig.  21  we  see  the  first  indication  of  stabilization.  The 
upper,  expanded  part  of  the  calyx  is  separated  from  a  conical,  lower  portion  by  a  slight 
groove.  The  marginal  lobes  have  become  semicircular  in  outline,  and  a  slight  elevation  is 
noticeable  on  the  aboral  side  of  each  rhopalial  tentacle  immediately  external  to  the  mass 
of  concretions.  The  epithelium  at  this  point  is  pigmented,  and  forms  the  first  rudiment 
of  the  eye  (oc.  Fig.  22) .  Fig.  23  illustrates  a  more  advanced  stage,  where  the  proximal 
part  of  the  tentacle  is  beginning  to  take  on  its  final  shape,  and  is  separated  by  a  pro- 
nounced bend  from  the  distal  portion,  which  is  still  functional  as  a  tentacle. 

We  come  finally  to  a  stage  in  which,  while  the  long  distal  part  of  the  tentacle  retains 
its  characteristic  structure  and  remains  completely  functional,  the  short  proximal  part 
has  become  completely  differentiated  into  a  rhopalium.  Fig.  54  is  from  a  longitudinal 
section  of  such  a  tentacle.  The  rhopalial  part  has  assumed  nearly  its  final  shape.  The 
differentiation  of  its  ectoderm  into  sensory  epithelium,  eye-spot,  and  layer  of  nerve  fibres, 
is  complete.  It  has  a  lumen  that  extends  outward  to  the  solid  chorda-like  endoderm  of  the 
distal  part  of  the  tentacle,  and  opens  toward  the  centre  into  a  gastric  pocket.  The  endo- 
dermal  lining  of  the  lumen  is  a  columnar  epithelium,  the  more  distal  cells  being  deeper 
and  containing  the  concretions.  Compare  Fig.  54  with  Fig.  53,  which,  being  interradial, 
was  certainly  destined  to  be  a  rhopalial  tentacle. 

The  growth  of  the  marginal  lobes,  which  were  semicircular  at  the  stage  of  Fig.  21, 
has  continued,  and  each  lobe  has  now  produced  two  secondary  ones,  one  on  each  side  of 
the  rhopalial  tentacle.  These  are  connected  by  a  slight  ridge  that  crosses  the  base  of  the 
tentacle  on  its  aboral  side  (h.  Fig.  54) .  The  secondary  lobes  are  the  rhopalial  lobes  of 
the  margin  of  the  umbrella  (Flugellappen  of  German  authors) ,  and  the  connecting  ridge 
is  the  hood  (Deckplatte)  that  covers  the  rhopalium.  These  marginal  structures  may  be 
seen  in  Fig.  24,  and  this  brings  us  to  another  stage  in  the  development  of  the  rhopalium, 
the  absorption  of  the  distal  part  of  the  tentacle. 

In  the  strobila  shown  in  Fig.  24,  the  rhopalial  tentacles  have  a  very  different 
appearance  from  what  we  have  seen  before.  They  are  shorter  than  the  other  tentacles, 
and  are  much  swollen  at  a  point  just  beyond  the  eye-spot.  The  distal  portion  is  begin- 
ning to  degenerate.  This  process,  when  once  begun,  proceeds  rapidly.  During  the  few 
hours  that  were  spent  in  making  this  drawing,  the  rhopalial  tentacles  were  reduced  in 
length  nearly  one  half.  The  eye-spots  and  concretions  were  conspicuous,  and  in  each  of 
the  former  there  was  a  slight  cup-shaped  depression.  This  is  the  earliest  stage  in  which  I 
observed  slight  medusa-like  movements  of  the  ephyra  disc.  The  tentacle  at  this  stage  is 
in  a  process  of  degeneration  for  about  fifteen  hundredths  of  a  millimeter  outward  from  the 
ocellus.  In  this  area  of  degeneration  (  t.  Fig.  55)  the  endodermal  cells  are  broken  down, 


CASSIOPEA   XAMACHANA.  221 

the  supporting  membrane  has  disappeared,  and  the  inner  boundary  of  the  ectoderm  is 
indistinct.  The  axial  mass  of  this  part  of  the  tentacle  is  made  up  of  loose  particles  of  a 
finely  granular  substance,  in  which  may  be  seen  many  small  and  deeply  stained  nuclei. 
There  are  also  a  number  of  green  cells  that  apparently  escaped  into  the  central  mass 
when  the  supporting  membrane  broke  down.  There  is  evidently  a  free  communication 
between  this  mass  of  disintegrating  material  and  the  digestive  cavity,  through  the 
rhopalial  canal. 

The  method  by  which  the  shortening  of  the  tentacle  is  brought  about  would  seem  to 
be  as  follows :  The  axial  cells  adjoining  the  cells  that  bear  the  concretions  (Fig.  54)  first 
break  down.  Why  they  should  do  so,  and  at  this  particular  time,  I  cannot  say.  This 
disintegration  proceeds  centrifugally,  and  it  is  accompanied  by  a  dissolution  of  the  sup- 
porting membrane.  The  ectodermal  cells  then  either  begin  here  and  there  to  break 
down  while  still  in  place,  and  the  resulting  debris  is  squeezed  into  the  central  cavity;  or 
else,  the  cells  migrate,  or  are  squeezed  inward  and  then  disintegrate.  The  continuity  of 
the  remaining  ectoderm  is  maintained,  however.  The  products  of  degeneration  prob- 
ably pass  through  the  rhopalial  canal  into  the  digestive  tract.  As  this  process  continues, 
the  inward  movement  of  the  ectodermal  cells  is  more  rapid  than  their  disintegration,  so 
that  when  the  distal  part  of  the  tentacle  is  reduced  to  the  size  of  the  rhopalial  part  (Figs. 
25  and  55),  it  is  a  solid  mass  of  small  cells  with  small  nuclei  that  stain  dark.  Some  of 
these  cells  contain  a  large  vacuole  and  have  the  nucleus  pushed  to  one  side.  Scattered 
among  the  small  cells,  there  are  a  number  of  globular  bodies  as  large  as,  or  larger  than, 
the  green  cells,  and  completely  filled  with  coarse  granules  that  stain  deeply  with  safranin; 
no  nucleus  is  visible  in  them.  The  ocellus  has  now  become  distinctly  cup-shaped  (oc. 
Fig.  55). 

At  about  this  time  the  interrhopalial  tentacles  begin  to  be  absorbed  in  their  turn 
(Fig.  25) .  The  umbrellar  margin  has  in  the  mean  time  grown  out  beyond  the  insertion 
of  each  interrhopalial  tentacle,  on  its  aboral  side,  into  two  lobes  with  a  hood  between 
(Figs.  25  and  26) .  This  structure,  although  smaller,  corresponds  exactly  to  the  rhopalial 
lobes  and  hood,  and  is  further  evidence  for  the  homology  between  the  tentacles  and  the 
rhopalia.  The  drawing  reproduced  in  Fig.  25  was  made  between  the  hours  of  eleven 
in  the  morning  and  two  in  the  afternoon.  At  five  o'clock  of  the  same  day  the  tentacles 
had  been  reduced  to  one  third  the  length  shown  in  the  figure,  and  the  absorption  of  the 
rhopalial  tentacles  was  very  nearly  completed. 

In  the  later  stages  of  the  absorption  of  the  interrhopalial  tentacles,  the  broken-down 
material  is  evidently  forced  in  some  way  into  the  radial  canal.  The  rhopalium  (Fig.  56) 
is  practically  complete  at  this  stage.  The  point  (x)  where  the  last  trace  of  the  tentacle 
proper  disappeared,  is  still  distinguishable  in  sections  by  the  presence  of  small  cells  with 
indistinct  cell  walls,  and  by  the  absence  of  otoliths. 


222  ROBERT    PAYNE    BIGELOW    ON 

These  observations,  then,  confirm  those  of  Glaus  ('83,)  who,  without  going  into  the 
details  of  development,  maintained  that  the  rhopalia  are  modified  basal  portions  of  the 
tentacles  of  the  scyphistoma;  and  they  contradict  Goette's  statement  that  the  rhopalia 
are  developed  independently  of  the  tentacles. 

Other  Phenomena  of  Stabilization. —  While  the  marginal  structures  are.  undergoing 
the  metamorphosis  that  has  just  been  described,  important  alterations  are  taking  place  in 
the  general  shape  of  the  body.  The  horizontal  constriction  first  noticed  in  Fig.  21  has 
deepened  (Fig.  24),  while  the  fold  below  it  has  heightened,  and  the  upper  portion  has  broad- 
ened and  flattened,  until  the  condition  shown  in  Fig.  26  is  reached.  At  this  final  stage 
the  upper  portion  has  all  the  characteristics  of  a  free-swimming  medusa  (ephyrula),  except 
that  it  is  attached  by  a  slender  aboral  stem  to  the  centre  of  a  goblet-shaped  basal  polyp. 
The  four  interradial  depressions  in  the  peristome  of  the  earlier  stages  have  become  nearly 
flattened  out,  all  that  remains  of  them  being  the  hollows  between  the  projecting  radial 
angles,  or  pillars,  of  the  proboscis,  which  have  now  become  very  prominent. 

At  the  stage  of  Fig.  21,  there  may  be  noticed  on  the  proboscis  eight  patches  of 
thickened  ectoderm  containing  many  nettle  cells.  These  nettle  batteries  are  arranged 
symmetrically,  one  on  each  side  of  each  pillar  of  the  proboscis.  At  a  little  later  stage 
(Fig.  24)  the  batteries  have  become  invaginated,  forming  cup-shaped  depressions,  thickly 
crowded  with  nettle  cells  in  all  stages  of  development. 

During  the  time  when  the  larva  is  being  differentiated  externally  into  an  upper  and 
a  lower  portion,  internal  changes  are  taking  place  in  the  former,  which  result  in  the 
disappearance  of  structures  characteristic  of  the  scyphistoma  and  the  appearance  of 
others  distinctive  of  the  medusa. 

The  orifices  in  the  gastric  septa  have  become  relatively  larger  (cs.  Fig.  52  and  re. 
Fig.  57)  until  the  septa  are  reduced  to  columnar  pillars,  columellae,  connecting  the  upper 
and  lower  walls  of  the  body  and  pierced  longitudinally  by  the  septal  muscles  (c.  Fig. 
58) .  The  columellae  are  called  by  German  authors  "Septalknoten,"  but  they  are  not 
homologous  with  the  so-called  "  Septalknoten,"  or  areas  of  adhesion,  in  the  Peromedusae. 
The  columellae  of  the  Peromedusae  are  the  walls  of  the  large  septal  funnels  where  they 
pass  from  the  subumbrella  to  the  exumbrella,  and,  according  to  Haeckel's  figures,  are 
separated  by  the  gonads  from  the  areas  of  adhesion. 

In  the  fully  developed  scyphistoma  of  Cassiopea,  the  septal  muscles  are  solid 
throughout  their  length,  and  there  is  no  cavity  corresponding  to  the  septal  funnels, 
which,  according  to  Goette,  are  well  developed  in  Aurelia.  But  in  the  strobila  there 
does  appear  a  slight  depression  extending  a  very  short  distance  into  the  end  of  each 
septal  muscle.  In  Figs.  57  and  58,  where  this  is  well  marked,  much  of  the  depression 
may  be  due  to  the  strongly  contracted  condition  of  the  specimens;  but  other  specimens 


CASSIOPKA   XAMACHANA.  223 

not  so  contracted  show  at  least  the  deeper-  part  of  the  cavity,  which  therefore,  may  be 
truly  a  vestige  of  the  septa!  funnel. 

At  an  early  stage  of  strobili/ation  there  may  be  noticed  a  short  conical  projection 
from  the  central  edge  of  each  eolumella.  It  extends  also  around  the  sides.  These  pro- 
jections are  probably  the  rudiments  of  the  first  four  gastric  filaments,  which  are  dis- 
tinctly developed  at  the  time  when  the  ephyrula  is  set  free  (<jf,  Fig.  58). 

While  the  septa  are  shrinking  to  become  the  columellae,  ridges  appear  opposite 
each  other  on  the  upper  and  lower  walls  of  the  peripheral  part  of  the  digestive  tract 
between  the  bases  of  the  tentacles.  The  epithelial  membranes  at  the  summits  of  oppo- 
site ridges  unite,  and  thus  there  is  formed  a  series  of  lines  of  adhesion  extending  inward 
from  the  periphery  and  dividing  the  space  into  a  series  of  radial  canals,  each  ending  in 
a  tentacle.  The  two  discs  of  mesogloea  never  fuse  along  these  lines  of  adhesion,  but  the 
endoderm  remains  between  them  as  the  endodermal  lamella,  or  cathammal  plate.  At  the 
stage  of  Fig.  24  the  lines  of  adhesion  occupy  about  half  the  space  from  the  margin  to 
the  columellae. 

The  lower  disc  of  the  strobila  remains  simply  an  annular  fold  of  the  body  wall  until  the 
metamorphosis  of  the  upper  disc  is  nearly  complete.  The  septa!  muscles  in  this  region 
bend  outward  with  the  rest  of  the  body  wall  (Fig.  57) .  At  length,  however,  the  endoderm 
grows  out  toward  the  periphery  as  four  shallow  pouches,  leaving  septa  between  them 
which  contain  the  longitudinal  muscles.  Very  soon  after  this  the  septa  are  perforated  so 
as  to  allow  a  fusion  of  the  endoderm  at  their  upper  angles  (Fig.  58).  In  the  last  stage 
of  stabilization  (Figs.  26  and  59)  the  longitudinal  muscles  may  be  traced  from  the 
peristorae  through  the  columellae  and  the  mesogloea  of  the  exuinbrella  to  the  narrow 
isthmus  where  the  ephyrula  disc  joins  the  basal  polyp.  The  latter  has  now  a  well- 
developed  peristome  (Fig.  59),  and  the  mesogloea  in  this  region  is  very  thin.  Just  in 
the  isthmus  the  muscles  have  disappeared,  but  they  may  be  found  again  in  the  peristome 
of  the  basal  polyp  and  traced  fora  distance  close  under  the  epithelium  to  the  edges  of 
the  septa,  where  they  bend  abruptly  downward,  and  continue  through  the  septa  into  the 
stem. 

Although  seldom  visible  in  the  living  specimen,  sections  show  that  the  basal  polyp 
at  this  sta-ge  possesses  eight  short  tenacles  (Fig.  59).  It  has  also  an  annular  fold  of  the 
ectoderm,  closely  surrounding  the  isthmus  (Fig.  59  and  p.  Fig.  60) .  This  fold  is  the 
rudiment  of  a  new  proboscis,  which  is  without  doubt  entirely  ectodermal  in  origin.  But, 
as  Goette  has  pointed  out,  it  does  not  follow  from  this  that  the  lining  of  the  proboscis  is 
ectodermal  in  scyphistomas  developed  from  the  egg.  Pulsating  contractions  of  the 
umbrella  are  first  noticed  at  the  time  when  the  rhopalial  tentacles  begin  to  be  absorbed 
(Fig.  24).  They  are  then  feeble  and  at  long  intervals.  At  the  stage  of  Fig.  26  these 


224  ROBERT   PAYNE   BIGELOW   ON 

I 

movements  are  rapid  and  violent.  The  rhythm  is  interrupted  by  few  pauses,  and  these 
are  short.  The  result  of  these  movements  is  that  the  thin  wall  of  the  isthmus  is 
ruptured,  and  the  ephyrula  is  set  free. 

After  this  separation,  the  basal  polyp  has  the  appearance  represented  in  Figs.  27  and 
28.  It  is  a  scyphistoma  with  seventeen  short  tentacles  and  a  rudimentary  proboscis 
(Figs.  61  and  62).  The  proboscis  and  the  tentacles  grow  rapidly,  so  that  in  a  few  days 
it  is  impossible  to  distinguish  a  regenerated  basal  polyp  from  a  young  scyphistoma  in  the 
sixteen-tentacle  stage,  except  that  the  former  has  a  somewhat  thicker  stem.  It  may  be 
inferred  from  this  complete  regeneration  of  the  basal  polyp  that  it  undergoes  repeated 
strobilization,  as  Glaus 1  has  found  to  be  the  case  in  Aurelia. 

The  Ephyrula.  —  The  ephyrula  of  Cassiopea  is  very  different  in  appearance  from  the 
corresponding  stage  in  ordinary  scyphomedusae  with  eight  rhopalia.  Cotylorhiza  has  an 
ephyrula  resembling  the  same  stage  in  the  semostomatous  medusae.  Good  figures  of 
this  are  given  by  du  Plessis  and  Glaus,  and  there  is  a  striking  difference  between  these 
figures  and  Figs.  29  and  30  in  this  paper,  which  are  camera  drawings  of  well-preserved 
ephyrulas  of  Cassiopea,  mounted  in  balsam.  Fig.  29  represents  a  young  Cassiopea  that 
has  not  long  enjoyed  a  free  existence.  The  general  shape  of  the  umbrella  is  like  that  of 
the  adult,  and  there  is  the  same  concavity  in  the  centre  of  the  exumbrella,  while  the 
margin  curves  in  the  opposite  direction,  as  in  Fig.  64.  The  typical  ephyrula  of  Aurelia 
or  Cotylorhiza  has  eight  marginal  arms  with  two  lobes  at  the  end  of  each,  and  between 
each  pair  of  lobes  there  is  a  rhopalium.  In  Cassiopea  structures  corresponding  to  these 
arms  are  present  to  the  number  of  sixteen,  or  often  more.  But  these  do  not  destroy  the 
general  circular  outline  of  the  animal,  for  they  are  connected  by  thin  areas  on  the 
umbrella,  alternating  with  an  equal  number  of  ridges,  which  at  an  earlier  stage  bore  the 
interrhopalial  tentacles  on  their  under  sides. 

We  have,  then,  at  this  stage  the  marginal  zone  of  the  umbrella  marked  by  a  number 
of  short  radial  ridges  separated  by  an  equal  number  of  thin  areas.  The  ridges  are  in 
line  with  the  radial  canals.  At  the  peripheral  end  of  each  ridge  the  margin  of  the 
umbrella  is  produced  into  two  lobes,  those  adjoining  the  rhopalia  being  well  marked, 
the  others  small  and  inconspicuous  (il.  Fig.  30). 

In  Fig.  29  there  are  seventeen,  and  in  Fig.  30,  twenty-three,  rhopalia.  The  latter 
is  an  unusually  large  number,  and  it  will  be  noticed  that  the  number  of  marginal  lobes 
has  not  increased  in  proportion,  so  that  irregularities  of  the  margin  occur  in  many  places, 
as  described  in  the  section  on  variations. 

At  this  stage  the  rhophalia  have  come  to  lie,  as  in  the  adult,  wholly  within  the  margin 
of  the  umbrella,  and  project  from  its  subumbrellar  surface.  The  interrhopalial  tentacles 

1  See  foot-no te,_Claus  ('92). 


CASSIOPEA   XAMACIIANA.  225 

have  totally  disappeared.     The  lines  of  adhesion  separating  the  radial  canals  are  faintly 
visible  as  radiating  lines  of  greater  transparency. 

The  fcmr  lips  of  the  mouth  are  spread  out  into  a  cross-shaped  figure,  and  one 
may  look  directly  through  the  lumen  of  the  oesophagus  into  the  stomach  and  see  the 
four  gastric  filaments  (Figs.  29  and  30).  Each  one  of  the  four  lips  is  nearly  square,  and 
from  its  two  outer  angles  there  are  two  grooves  that  extend  obliquely  inward  until  they 
meet  and  form  a  V.  The  point  of  the  V  is  in  an  angle  of  the  oesophagus,  along  which 
there  is  a  groove  that  is  continuous  with  the  other  two  grooves,  and  that  extends  into 
the  stomach.  On  the  interradial  side  of  each  of  the  eight  labial  grooves,  there  may  be 
seen  a  small  roughly  circular  area  that  is  less  transparent  than  the  rest.  These  areas  are 
the  nettle  batteries,  first  seen  in  the  strobila.  The  margins  of  the  lips  are  provided 
with  numerous  small  processes,  the  drgitella,  which  are  arranged  in  a  single  continuous 
series. 

Fig.  63  is  a  section  of  an  ephj^rula  that  has  just  become  free.  In  this  stage  there  is 
still  an  opening  through  the  aboral  wall  of  the  stomach,  and  one  may  see  the  last  vestige 
of  the  connection  between  the  columella  and  the  exumbrella,  which  contains  also  the 
degenerating  remnants  of  the  septal  muscle. 

At  a  little  later  stage,  when  the  opening  in  the  roof  of  the  stomach  has  closed, 
both  the  septal  muscles  and  the  septal  funnels  totally  disappear.  Sometimes  one,  some- 
times the  other,  is  the  first  to  vanish. 

The  Later  Stages.  —  The  later  stages  in  the  development  of  Cassiopea  will  be 
treated  very  briefly.  While  the  umbrella  remains  at  first  unchanged,  the  metamor- 
phosis of  the  mouth  parts  is  inaugurated  by  the  growth  of  the  two  outer  angles  of  each 
of  the  more  or  less  quadrate  lips,  so  that  they  [are  soon  drawn  out  into  extended  lobes 
(Fig.  31).  At  the  same  time  the  pillars  of  the  proboscis  thicken,  and  the  mesogloea  is 
continued  outward  along  each  of  these  lobes  as  a  midrib.  We  have  then  eight  oral 
arms,  each  with  a  longitudinal  groove,  supported  by  a  midrib,  and  fringed  with  digi- 
tella, —  arms  very  similar  to  those  characteristic  of  the  genus  Aurosa  Haeckel  ('79) .  But 
it  is  only  the  mouth  parts  of  Cassiopea  that  may  be  said  to  pass  ^through  an  Aurosa  stage, 
for  the  comparison  cannot,  at  this  time  at  least,  be  carried  to  the  other  organs. 

Glaus  has  described  ('83)  some  of  the  principal  stages  in  the  metamorphosis  of  Pilema 
(Rhizostoma)  and  Cotylorhi/a.  He  regards  the  formation  of  the  eight  oral  arms  as  a  dif- 
ferent process  in  these  forms  from  what  occurs  in  Aurosa.  But  it  appears  to  be  merely  the 
same  thing  expressed  differently. 

In  the  next  stage  we  find  two  oral  funnels,  or  oscula,  and  a  small  vesicle  developed  at 
the  tip  of  each  oral  arm.  The  other  portions  of  the  arm  are  still  open  and  fringed  with 
digitella,  as  before,  but  the  outline  is  no  longer  a  regular  curve,  for  there  are  folds  in  the 


226  ROBERT    PAYNE    15KJELOW    ON 

margin.  The  deepest  folds  are  the  most  distal,  and  they  become  progressively  more 
shallow  toward  the  base  of  the  arm.  The  central  mouth  is  still  widely  open.  The  subgeni- 
tal  cavities  are  well  developed  at  this  stage.  Figs.  64,  65,  and  66  show  how  the  oral  disc 
is  formed,  and  how  the  subgcnitsil  cavities  are  produced  by  the  great  increase  in  thickness 
of  the  mesogloea  at  the  pillars  of  the  proboscis  and  the  bases  of  the  oral  arms.  By  the 
growth  of  these  structures,  the  subgenital  cavities  are  necessarily  produced.  The  only 
special  adaptations  are  the  subsequent  growth  and  folding  of  the  aboral  wall  and  the 
narrowing  of  the  orifice. 

The  marginal  lobes  of  the  umbrella  now  begin  to  broaden,  and  thus  approach  the 
adult  condition,  but  there  is  only  a  single  "vellar"  lobe  between  two  rhopalial  ones. 

At  a  little  later  stage,  when  there  are  three  oral  funnels  at  the  tips  of  the  arms 
(Fig.  33),  the  re-entrant  angles  between  the  pillars  of  the  proboscis  have  grown  inward, 
met  at  the  centre,  and  fused.  In  this  Avay  the  lumen  of  the  oesophagus  is  divided 
into  four  tubes  (Fig.  32) ,  representing  the  grooves  that  were  present  in  its  angles  in  the 
earlier  stages.  In  the  figure  the  fusion  at  the  centre  has  gone  so  far  as  to  involve  the 
edges  of  the  lips,  and  the  labial  grooves  of  the  different  pairs  of  arms  are  not  in  open 
communication,  but  a  short  cross-shaped  tube  connects  them  at  the  centre,  and  the  oral 
disc  is  now  completed. 

It  is  interesting  to  note  that  Clans  has  found  a  stage  both  in  Pilema  and  in  Coty- 

• 

lorhiza  that,  while  showing  the  characteristic  family  differences,  has  also  a  certain 
resemblance  to  this  stage  in  Cassiopea.  In  all  three  the  walls  of  the  proboscis  have  fused 
so  as  to  divide  its  lumen  into  four  tubes,  and  the  formation  of  oscula  has  begun  at  the  tips 
of  the  arms  in  such  a  way  that  we  have  on  each  arm  three  oscula  with  a  vesicle  in  the 
angles  between  them.  The  occurrence  of  this  stage  in  the  ontogeny  of  three  so  distinctly 
separated  families  must  have  some  morphological  significance,  and  we  may  regard  these 
eight  primary  vesicles  as  homologous  in  the  three  groups. 

The  mode  of  formation  of  the  oral  funnels  becomes  evident  at  this  stage.  They  are 
not  formed  in  Cassiopea  simply  by  a  series  of  fusions  of  the  lips  along  the  line  of  the 
labial  groove,  as  Hamann  ('8l)  states  to  be  the  case  in  Cotylorhiza.  It  is  more  like  the 
process  in  Pilema,  as  described  by  Clans.  Each  of  the  primary  funnels  is  represented  at 
first  by  one  of  the  folds  in  the  margin  of  the  lips  referred  to  above  (Fig.  33) .  The 
fold  deepens,  and  its  edges  are  brought  together  on  the  ventral  side  and  fuse,  leaving  an 
opening  at  the  apex  of  the  fold,  the  osculum.  At  the  same  time  the  labial  groove  in 
this  region  is  converted  into  a  canal  by  the  fusion  of  the  lips  on  its  two  sides.  After 
the  fusion  all  trace  of  what  has  occurred  quickly  disappears. 

Witli,  the  division  of  the  oesophagus  into  four  tubes,  and  the  completion  of  the  oral 
disc,  our  larva  comes  to  be  distinctly  a  rhizostomatous  medusa.  Further  development  of 


CASSIOPEA    XAMACUANA.  227 

the  mouth  parts  consists  in  the  continued  division  of  the  labial,  or  brachial,  grooves  into 
oral  funnels  and  brachial  canal,  together  with  the  development  of  oral  vesicles.  By  the 
time  two  or  three  vesicles  have  been  formed  on  the  end  of  each  arm,  a  vesicle  appears  in 
the  centre  of  the  oral  disc.  Except  for  this  interruption,  the  development  of  the  mouth 
parts  proceeds  regularly  in  a  centripetal  direction.  The  funnels  and  vesicles  are  formed 
lirst  at  the  tips  of  the  arms,  and  then  one  after  another  in  regular  succession  toward  the 
centre.  Each  of  these  primary  funnels  is  the  rudiment  of  one  of  the  primary  branches  of 
the  arm.  When  the  process  of  forming  funnels  has  reached  about  half  the  length  of  the 
arm,  the  distal  funnels  begin  to  subdivide.  By  this  subdivision  of  the  primary  funnels 
new  ones  are  produced,  of  which  some  are  the  rudiments  of  secondary  branches  ;  these  sub- 
divide again,  and  so  on,  as  long  as  growth  continues.  The  subdivision  is  not  dichotomous, 
but  takes  place  in  such  a  way  as  to  produce  alternate  branches.  The  formation  of  a 
vesicle  takes  place  at  this  stage  in  some  way  at  about-  the  time  of  the  completion  of  the 
adjoining  funnel.  I  have  not  been  able  to  determine  whether  the  vesicle  is  a  funnel  with 
(lie  orifice  closed,  as  Ilamanu  claims  it  to  be,  or  whether  it  is  an  evagination  from  the 
pedicle  of  a  funnel,  as  at  first  it  seemed  to  me  to  be,  and  as  Glaus  thinks  it  probably  is. 

According  to  Haeekel  ('79),  the  genus  Archirhiza  represents  a  form  that  was  the 
ancestor  of  all  the  rhizostomatous  medusae.  Of  this  genus  there  are  two  known  species, 
A.  primordiafis  Haeekel,  and  A.  miroxa  Haeekel.  They  agree  in  having  four  subgenital 
cavities  and  eight  simple  unbranched  arms  that  are  provided  with  a  single  zig-zag  row  of 
closely  set  oral  funnels,  and  are  devoid  of  other  appendages.  Hamann  says  that  a  stage 
representing  this  condition  is  a  feature  of  the  ontogeny  of  rhizostomatous  medusae.  From 
what  has  been  said  it  is  evident  that  we  have  no  such  stage  in  the  development  of  Cassi- 
opea  xamachana,  for  while  the  labial  groove  is  still  open  in  the  proximal  half  of  the  oral 
arm,  in  its  distal  half  the  vericles  are  formed,  and  branches  are  in  the  process  of 
formation. 

The  outline  of  the  umbrellar  margin  has  not  changed  essentially  since  the  last  stage. 
The  areas  of  adhesion  have  become  much  wider  than  the  radial  canals  they  separate,  and 
in  them  there  has  appeared  a  network  of  anastomosing  canals,  while  the  gastric  filaments 
have  become  numerous. 

We  have  now  followed  the  larva  of  our  Cassiopea  from  its  first  appearance  as  a  bud 
to  a  point  where,  with  the  exception  of  the  gonads,  all  the  organs  of  the  adult  are  out- 
lined. Here  we  must  take  leave  of  it. 


228  ROBERT    PAYNE    BIGELOW    ON 

SUMMARY  AND  CONCLUSIONS. 

Cassiopea  and  Polyclonia  are  genera  of  rhizostomatous  medusae  peculiarly  modified  in 
adaptation  to  a  sedentary  mode  of  life  in  shallow  water  among  the  mangroves  bordering 
tropical  seas.  A  comparison  of  specimens  of  Polyclonia  frondosa  Ag.  with  Cassiopea 
xamachana  shows  that  these  two  forms  are  specifically  distinct,  although  in  general 
appearance  they  are  very  similar  and  they  have  the  same  geographical  range  and 
habitat. 

C.  xamachana  is  remarkable  for  its  variability.  This  is  especially  shown  in  the 
appendages  to  the  mouth  parts  and  in  the  structures  at  the  margin  of  the  umbrella.  It 
will  be  noticed  that  the  most  frequent  number  of  rhopalia,  in  the  twenty-seven  specimens 
examined,  was  sixteen,  which  is  the  typical  number  for  the  genus.  But  the  variations  are 
hot  arranged  symmetrically  on  the  two  sides  of  this  mode,  for  specimens  having  a 
greater  number  of  rhopalia  are  more  than  twice  as  many  as  those  having  less.  The 
species  shows  a  strong  tendency  toward  duplication  of  the  rhopalia  and  associated  struc- 
tures of  the  umbrella ;  and  at  the  same  time  the  symmetrical  relations  of  the  parts  tend 
to  be  preserved.  The  great  majority  of  scyphomedusae  have  only  eight  rhopalia,  and  in 
Cassiopea  with  its  sixteen  rhopalia  we  have  a  beautiful  illustration  of  Darwin's  law  that 
"  A  part  developed  in  any  species  in  an  extraordinary  degree  or  manner,  in  comparison 
with  the  same  part  in  allied  species,  tends  to  be  highly  variable."  Study  of  the  color 
markings  and  measurements  of  the  mouth  parts  indicates  the  division  of  the  species  into 
three  varieties;  and  it  was  in  one  of  these,  var.  A,  that  the  duplication  of  marginal  organs 
was  especially  prevalent. 

The  color  of  both  larvae  and  adults  is  due  to  a  great  extent  to  the  presence  in  the 
mesogloea  of  minute  symbiotic  algae.  That  these  are  plant  cells  was  demonstrated  by 
micro-chemical  tests.  Their  presence  undoubtedly  enables  the  medusae  to  live  in  water 
that  would  be  too  poor  in  oxygen  for  most  marine  animals. 

The  search  for  developing  eggs  proved  unsuccessful,  but  scyphistoma  larvae  were 
abundant,  and  it  was  found  that  they  were  multiplying  rapidly  by  budding. 

The  bud  arises  as  an  evagination  of  the  body  wall  of  the  scyphistoma.  There  is  no 
evidence  of  any  special  gemminal  epithelium.  The  bud,  when  set  free,  differs  from  a 
planula  chiefly  in  the  possession  of  a  well-defined  mesogloea  and  four  septal  muscles.  The 
septal  muscles  are  shown  to  be  formed  as  branches  of  the  two  adjacent  septal  muscles  of 
the  parent.  The  mouth  of  the  young  scyphistoma  is  formed  by  a  minute  perforation  at, 
the  former  point  of  attachment,  while  the  distal  end  of  the  bud  becomes  the  stem.  This 
remarkable  orientation  agrees  with  what  Goette  and  Clans  have  found  in  Cotylorhita,  In 


CASSIOPEA   XAMACHANA.  229 

the  formation  of  the  mouth  there  is  no  evidence  of  any  invagination  of  ectoderm  Ap- 
parently the  oesophagus,  as  well  as  the  gastric  pouches,  is  lined  with  endoderm.  On 
the  other  hand,  the  oesophagus  of  the  lower  disc  of  the  strobila  is  formed  wholly  of 
ectoderm. 

The  four  radial  tentacles  are  formed  simultaneously,  and  the  four  interradial  ones 
appear  at  the  same  time  or  slightly  later.  These  are  followed  by  eight  adradinl  tentacles 
and  sixteen  more  are  added  a  little  later,  making  thirty-two  in  all.  It  was  found  that  the 
rudiments  of  the  interradial  tentacles  are  not  at  all  constant  in  position  with  relation 
to  the  septa.  Some  were  septal,  others  were  interseptal,  sometimes  on  one  side  of  the 
septum,  sometimes  on  the  other,  thus  agreeing  with  the  observations  of  Glaus  on  Aurelia 
and  Cotylorhiza. 

The  four  gastric  pouches  are  formed  at  the  same  time  by  the  ingrowth  of  the  septa. 
They  are  soon  brought  into  communication  at  the  periphery  by  the  perforation  of  the 
septa,  which  become  reduced  to  columellae  surrounding  the  longitudinal  muscles. 

Contrary  to  Goette's  opinion,  it  may  be  staled  positively  that  the  rhopalia  are  differ- 
entiated in  the  bases  of  alternate  tentacles.  After  the  rhopalium  is  fully  developed,  the 
distal  part  of  the  tentacle  undergoes  degeneration  and  is  absorbed.  The  development  was 
traced  for  the  first  time  through  all  its  stages,  and  the  opinions  of  Agassiz,  Claus,  and 
Lendenfeld  are  fully  confirmed. 

The  scyphomedusae  are  the  only  coelente rates,  which  possess  four  longitudinal 
muscles  of  ectodermal  origin  completely  imbedded  in  the  mesogloea  between  the  points  of 
insertion.  The  buds  of  Cassiopea  have  this  distinctively  medusoid  characteristic  long 
before  they  are  detached.  Moreover,  the  methods  by  which  the  mouth  and  the  gastric 
pouches  are  formed  differ  entirely  from  what  is  said  to  take  place  in  larvae  that  pass 
through  an  anthozoan  stage.  Therefore,  whatever  may  be  true  of  the  larvae  derived  from 
eggs,  this  stage  is  certainly  omitted  in  larvae  produced  by  budding. 

The  first  step  toward  the  formation  of  the  free-swimming  medusa  is  the  perforation 
of  the  gastric  septa  which  takes  place  in  the  young  scyphistoma  before  it  is  fully 
developed.  Then  follows  a  period  of  growth  and  reproduction  by  budding,  and  further 
metamorphosis  begins  finally  with  the  process  of  strobilization.  Besides  the  differentia- 
tion of  the  sense  organs  and  the  development  of  the  marginal  lobes  of  the  umbrella,  the 
most  important  events  are  the  development  of  the  angles  of  the  mouth  into  quadrate 
lobes  and  the  fusion  of  the  two  layers  of  endoderm  along  certain  areas  of  adhesion  so  as 
to  divide  the  periphery  of  the  digestive  tract  into  a  series  of  radial  canals.  Only  one 
medusa  is  formed  ;  but,  separated  from  this  by  a  constriction,  is  a  small  basal  segment 
which,  a  short  time  before  the  medusa  becomes  free,  begins  to  develop  gastric  pouches, 
tentacles,  and  a  proboscis.  This  becomes  eventually  a  perfect  scyphistoma,  and  after  a 
period  of  growth  probably  undergoes  stabilization  again. 


230  ROBERT   PAYNE   BIGELOW   ON 

There  has  been  considerable  discussion  in  regard  to  the  nature  of  stabilization;  the 
question  being  whether  the  medusa  is  to  be  regarded  as  a  metamorphosed  scyphistoma, 
or  as  derived  from  the  scyphistoma  by  a  process  of  budding.  In  the  monodiscous  strobila 
of  Cassiopea  we  have  clearly  a  metamorphosis.  The  form  of  the  medusa  is  the  result  of  a 
series  of  changes  which  begin  very  early  and  involve  all  the  essential  organs  of  the  scy- 
phistoma. The  portion  not  involved  in  these  changes  merely  serves  as  a  mechanical  sup- 
port. That  this  part  is  separated  off  and  regenerates  the  lost  parts,  instead  of  being 
absorbed,  may  be  regarded  as  merely  an  incidental  fact. 

If  there  be  any  question  of  budding  it  refers  to  this  basal  segment.  And  this  suggests 
a  striking  analogy  between  the  basal  polyp  and  the  peculiar  planula-like  buds.  In  the 
first  place  they  have  the  same  orientation  relative  to  the  upper  disc.  In  both,  the  distal 
end  forms  the  stem  and  the  proximal  end  forms  the  mouth.  In  the  second  place,  they 
have  essentially  the  same  structure.  Each  one  consists  of  a  simple  sac  with  a  wall  made 
up  of  three  layers,  ectoderm,  mesogloea  and  endoderm,  and  each  is  provided  with  four  longi- 
tudinal muscles  imbedded  in  the  mesogfoea.  What  differences  appear  in  the  subsequent 
development,  may  be  attributed  to  the  different  ways  in  which  the  two  become  separated 
from  the  disc  and  to  the  greater  size  of  the  longitudinal  muscles  in  the  basal  polyp.  The 
production  of  supernumerary  tentacles,  rhopalia,  and  marginal  lobes,  is  common  in  this 
species.  Why  may  we  not  regard  the  buds  as  supernumerary  basal  polyps,  and  their 
subsequent  development  as  a  process  of  regeneration  preserved  and  modified  by  natural 
selection  for  its  obvious  advantage? 

The  ephyrula  of  Cassiopea  has  the  same  number  of  rhopalia  as  the  adult,  and  differs 
in  shape  from  the  corresponding  stage  of  ordinary  scyphomedusae  with  eight  parameres. 

The  most  important  event  in  the  later  stages  is  the  metamorphosis  of  the  mouth 
parts.  The  angles  of  the  four  quadrate  lips  become  extended  to  form  eight  oral  arms 
somewhat  similar  to  those  found  in  the  adult  Aurosa.  There  is  no  Archirhiza  stage,  but 
there  follows  a  stage  with  the  oesophagus  divided  into  four  tubes,  and  with  three  oscula 
and  an  oral  vesicle  on  each  arm.  A  similar  stage  has  been  found  in  Pilema  and  Coty- 
lorhiza,  and  it  may  have  some  phylogenetic  significance. 

The  studies  of  numerous  investigators  upon  the  Ascidians  have  demonstrated  that  a 
knowledge  of  the  gamogenetic  development  of  an  animal  will  not  always  enable  one  to 
predict  how  the  organs  will  be  formed  in  the  agamogenetic  process.  So  it  may  be 
objected  that  the  results  set  forth  in  this  paper  do  not  afford  a  valid  basis  for  the  criticism 
of  work  done  by  others  on  larvae  developed  from  the  egg.  On  the  other  hand,  the  eight- 
tentacle  stage  of  the  bud  larva  of  Cassiopea  is  so  like  the  same  stage  of  the  sexually  pro- 
duced larva  of  its  near  relative  Polyclonia  that  it  would  be  impossible  to  tell  them  apart, 
and,  in  the  absence  of  any  evidence  to  the  contrary,  there  seems  to  be  no  necessary  reason 


CASSIOPEA  XAMACHANA.  231 

for  supposing  that  their  later  history  is  different.  At  any  rate,  we  have  here  the  first 
fairly  complete  history  of  the  development  of  a  scyphomedusa  from  the  bud;  and  when 
the  sexual  development  of  Cassiopea  xamachana  or  an  allied  species  is  studied,  this 
memoir  will  serve  as  a  means  of  comparison,  and  will  make  it  possible  to  determine 
whether  or  not  the  two  modes  of  ontogeny  are  alike. 


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233 


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EXPLANATION  OF  PLATES. 

All  the  figures  from  I  to  28,  and  Figs.  34  and  35,  are  freehand  drawings  made  from  the  living  animals.  Figs.  29  to 
33  are  from  well-preserved  specimens  mounted  in  balsam,  and  were  outlined  with  the  camera  lucida.  The  remaining  figures, 
except  Fig.  37,  are  camera-lncida  drawings  of  microtome  sections.  All  the  figures  are  reduced  uniformly  to  slightly  less 
than  one  half  the  diameter  of  the  original  drawings. 


LETTERING  COMMON  TO   ALL  THE   FIGURES. 


b.  — bud. 

c.  —  columella. 

c  d.  —  circum-oral  disc,  or  peristome. 

cs.  —  circular  sinus. 

ex.  —  calyx. 

d. — digitellum. 

ect.  —  ectoderm. 

e  1.  — endodermal  lamella,  or  cathammal  plate. 

end.  —  endoderm. 

e  u.  —  exumbrella. 

g. —  stomach. 

g  f .  —  gastric  filament. 


g  p.  —  gastric  pouch. 

h.  —  hood. 

i  1.  —  interrhopalial  lobe. 

i  t.  — interrhopalial  tentacle. 

1  g.  —  labial  groove. 

m.  —  mouth. 

mes.  — mesogloea,  or  supporting  membrane. 

n  f.  — nerve  fibres. 

o  a.  — oral  arm. 

oc.  —  ocellus. 

o  d.  —  oral  disc. 

oe.  —  oesophagus. 


234 


ROBERT    PAYNE    BIGELOW    ON 


oe.  t.  —  oesophageal  tube,  or  canal. 

os.  — osmium. 

ot.  — rhopalial  concretion  (otulitli). 

p.  —  proboscis. 

p  p.  —  pillar  of  the  proboscis. 

r  c.  —  radial  canal. 

rh.  —  rhopalium. 

rh.  c.  —  rhopalial  canal. 

rh.  t. — rhopalial  tentacle. 

s.  —  stem. 


s  e.  —  sensory  epithelium. 

sep.  —  septum. 

s  f.  — septal  funnel. 

s  g.  —  subgenital  cavity. 

s  in.  —  septal  muscle. 

s  u.  —  subumbrella. 

t.  —  tentacle. 

v.  —  vesicle. 

za. — brownish  green  cells,  symbiotic  algae. 


PLATE   31. 

Fig.  1.  Portion  of  the  calyx  and  stem  of  a  scyphistoma  with  a  fully  developed  bud  (ft)  attached.  A,  the  outline  of  the 
same  bud  when  contracted. 

Fig.  2.  Similar  to  the  preceding,  except  for  the  formation  of  a  second  bud  (ft')  which  bears  the  older  one  (ft)  upon  its 
apex. 

Fig.  3.  The  form  of  the  plamila-like  bud  during  the  first  tw,>  days  after  becoming  free.  A,  B,  and  C,  are  the  successive 
changes  in  shape  observed  in  one  specimen  during  a  few  minutes.  The  arrows  show  the  direction  in  which  it  swims. 

Fig.  4.       Larva  of  probably  the  third  day.     A,  lateral  aspect;  B,  oral  aspect. 

Fig.  5.       A  larva  of  about  the  same  age,  48  hours  or  over. 

Fig.  6.      Another  larva  of  48  hours  or  over. 

Fig.  7.       Larva  of  the  fourth  day.. 

Fig.  8.  Free  scyphistoma  of  the  fifth  day,  with  rudiments  of  four  tentacles.  The  arrows  show  the  direction  of  progres- 
sion and  rotation. 

Fig.  0.       A  scyphistoma  of  about  the  same  age,  with  the  rudiments  of  eight  tentacles. 

Fig.  10.     Oral  aspect  of  a  similar  larva,  perhaps  somewhat  younger. 

Fig.  11.     A  scyphistoma  a  little  mare  advanced,  probably  in, the  fifth  day. 

Fig.  12.  A  still  more  advanced  scyphistoma  of  the  fifth  day.  The  four  tentacles  first  formed  are  much  longer  than  the 
other  four. 

Fig.  13.     Scyphistoma  of  the  sixth  day,  attached,  and  with  eight  tentacles. 

Fig.  14.  Scyphistoma  with  rudiments  of  the  second  set  of  eight  tentacles.  Two  tentacles  of  the  first  series  are  bifur- 
cated. 

Fig.  15.     Scyphistoma  with  sixteen  tentacles  fully  developed,  in  tile  attitude  of  feeding. 

Fig.  16.     Oral  aspect  of  a  similar  specimen. 


PLATE   32. 


Fig.  17.  Scyphistoma  showing  first  traces  of  rhopalial  structure. 

Fig.  18.  A  small  portion  of  the  margin  more  highly  magnified. 

Fig.  19.  Scyphistoma  at  a  slightly  older  stage. 

Fig.  20.  Small  part  of  the  margin  of  a  similar  larva. 

Fig.  21.  An  early  stage  in  strobilization. 

Fig.  22.  A  rhopalial  tentacle  of  the  same  specimen  seen  from  the  side. 

Fig.  2.3.  An  older  rhopalial  tentacle. 

Fig.  24.  Strobila  in  which  the  rhopalial  tentacles  have  begun  to  degenerate. 


CASSIOPEA   XAMACHANA.  235 


PLATE  33. 

Kite.  26.  Strobila,  in  whicli  the  degeneration  of  the  rhopalial  tentacles  is  nearly  completed,  and  the  interrhopalial 
tentacles  have  begun  to  degenerate. 

Fiji.  '26.  A  complete  strobila.  The  basal  polyp  bears  a  bud  which  broke  off  and  swam  away  while  the  drawing  was 
being  made.  The  ephyrula  was  detached  during  the  following  night.  The  rhopalia  are  visible  through  the  umbrella. 
At  y,  is  a  pair  of  twin  rhopalia  ;  compare  y,  Fig.  30. 

Fig.  27.     Tue  basal  polyp  of  the  same  specimen,  a  few  hours  after  the  separation  of  the  ephyrula. 

Fig.  28.     Optical  section  of  the  same. 

Fig.  29.     An  ephyrula  recently  set  free.     Oral  aspect.     The  gastric  filaments  are  visible  through  the  mouth,     x  31. 

Fig.  30.     A  specimen  of  about  the  same  age,  showing  variations  of  the  margin  at  u,  w,  x,  y  and  z.     X  31. 

PLATE   34. 

Fig.  31.  Mouth  parts  of  a  young  medusa  in  the  Aurosa  stage.  The  gastric  filaments  may  be  seen  through  the  central 
mouth  opening.  X  33. 

Fig.  32.  Oral  disc  of  an  older  specimen.  The  oesophageal  tubes  appear  as  light  areas,  one  at  the  junction  of  each  pair 
of  labial  grooves. 

Fig.  33.     One  of  the  oral  arms  from  the  same  specimen  as  Fig.  32. 

Fig.  34.  Floor  of  the  stomach  and  the  oral  arms  of  an  adult  viewed  from  the  aboral  side.  The  roof  of  one  subgenital 
cavity  is  removed,  and  a  threat!  is  represented  as  passing  through  the  external  orifice  into  this  cavity,  at  x.  The  ultimate 
branches  are  represented  on  only  one  of  the  oral  arms. 

Fig.  35.    Portion  of  the  aboral  surface  of  an  adult.     About  half  natural  size. 

PLATE   35. 

Fig.  36.     Section  of  a  young  bud.     X  Zeiss  DD  +  oc.  2.' 

Fig.  37.  Diagram  to  show  the  branching  of  the  septal  muscles,  SHI,,  am,,  sm3  and  xmt,  and  the  connections  of  the 
septal  muscles  of  the  bud,  sm',,  sm'n,  and  «?«'.,.  Reconstructed  from  the  series  of  sections  of  which  Fig.  36  is  one.  • 

Fig.  38.  Section  through  the  distal  apex  of  an  older  bud,  showing  the  attachment  of  a  septal  muscle  to  the  ectodennal 
epithelium.  X  Zeiss  II  +  oc.  2. 

Fig.  39.  Longitudinal  section  of  a  planula-like  larva.  D  was  the  distal,  and  P  the  proximal,  end  of  the  bud  while 
attached.  X  Zeiss  DD  +  oc.  2,  dt.  ICO. 

Fig.  40.  Longitudinal  section  through  the  posterior  end  of  a  swimming  larva,  in  which  changes  preparatory  to  the 
formation  of  the  mouth  are  taking  place.  X  B  &  L  i  +  Zeiss  oc.  2. 

Fig.  41.  Similar  section  of  a  slightly  older  larva,  showing  the  mo.uth  as  a  small  opening  not  exceeding  in  width  the 
thickness  of  the  section.  X  B  &  L  J  +  Zeiss  oc.  2,  dt.  160. 

Fig.  42.     Adradial  section  of  a  scyphistoma  a  little  older  than  Fig.  9  (5th  day).     X  Zeiss  DD  +  oc.  2. 

Fig.  43.  Obliquely  transverse  section  of  a  specimen  of  the  same  age,  showing  the  greatest  width  of  one  septum.  X  B 
&  L  J  +  Zeiss  oc.  2,  dt.  160. 

Fig.  44.  A  tangential  section  of  an  older  larva,  showing  the  connection  of  a  septal  muscle  with  the  circum-oral  disc. 
X  Zeiss  H  +  oc.  2. 

PLATE   36. 

Figs.  45  to  47  are  consecutive  transverse  sections  of  one  individual.  Fig.  45  shows  the  continuity  between  the  endoderm 
of  adjacent  gastric  pouches  at  the  base  of  an  interradial  tentacle.  Fig.  47  is  lower,  and  here  the  gelatinous  septum  com- 
pletely separates  the  two  pouches.  X  Zeiss  H  +  oc.  2. 

1  Unless  otherwise  noted,  the  microscope  was  used  with  the  draw  tube  not  drawn  out.    Length  of  tube  (dt.)  =  1ST  mm. 


-236  ROBERT   PAYNE    BIGELOW    ON    CASSIOPEA    XAMACHANA. 


Figs.  48  and  49  are  from  the  same  series.  Fig.  48  is  the  second  section  below  Fig.  47.  It  just  clears  the  oesophagus. 
Fig.  49  is  through  the  upper  part  of  the  stem.  X  Zeiss  DD  -f  oc.  2. 

Fig.  50.  Longitudinal  section  of  a  scyphistoma  with  sixteen  tentacles,  probably  a  little  younger  than  Fig.  15.  X  Zeiss. 
DD  +  oc.  2,  dt.  195. 

Fig.  61.  An  obliquely  transverse  section  of  a  fully  developed  scyphistoma,  showing  the  relations  of  the  septal  muscles 
to  the  depressions  in  the  circumoral  disc.  The  mesogloea  is  shaded.  X  Zeiss  B  +  oc.  2,  dt.  ICO. 

Fig.  52.  Part  of  an  interradial  section  from  a  scyphistoma  a  little  older  than  the  last.  Owing  to  a  slight  obliquity  of 
the  section,  the  full  extent  of  the  circular  sinus  at  the  base  of  the  tentacle  is  not  shown.  It  extends  to  the  point  marked  x. 
X  Zeiss  C  +  oc.  2. 


PLATE   37. 

Figs.  63  to  56  illustrate  the  development  of  the  rhopalia. 

Fig.  53.  Median  section  of  the  interradial  tentacle  shown  in  Fig.  52  ;  x  marks  a  corresponding  point  in  the  two  sections 
X  Zeiss  H  +  oc.  2. 

Fig.  54.   A  radial  section  from  the  base  of  a  rhopalial  tentacle  somewhat  older  than  Fig.  23.     X  Zeiss  H  +  oc.  2. 

Fig.  55.   Radial  section  of  a  rhopalium  in  the  stage  of  Fig.  25.     x  Zeiss  H  -}-  oc.  2. 

Fig.  56.   Radial  section  of  a  rhopalium  in  about  the  stage  of  Fig.  26.     X  Zeiss  H  +  oc.  2. 

Fig.  57.   Radial  section  showing  the  course  of  a  septal  muscle  in  a  strobila,  at  the  stage  of  Fig.  24.     X  ZeLss  DD  +  oc.  2. 

Fig.  58.  A  similar  section  from  a  specimen  a  little  older  than  Fig.  25  ;  x,  point  of  separation  between  the  two  discs. 
X  Zeiss  DD  +  oc.  2. 

PLATE   38. 

Fig.  69.  Median  vertical  section  of  a  strobila  in  the  stage  of  Fig.  26 ;  x,  boundary  between  ephyrula  and  basal  polyp. 
X  Zeiss  B  +  oc.  2. 

Fig.  60.  Portion  of  section  from  the  same  specimen,  showing  the  proboscis  of  the  basal  polyp  ;  x  marks  same  point  as 
in  preceding.  X  B  &  L  |  +  Zeiss  oc.  2,  dt.  160.  t 

Fig.  61.   Median  vertical  section  of  a  basal  polyp,  stage  of  Fig.  27.     X  Zeiss  B  -f-  oc.  2. 

Fig.  62.  Part  of  a  section  from  the  same  specimen,  showing  the  proboscis,  p,  and  the  vestige  of  the  former  connection 
with  the  ephyrula  at  x.  X  B  &  L  £  +  Zeiss  oc.  2,  dt.  160. 

Fig.  63.  Median  vertical  section  of  an  ephyrula  that  has  recently  become  free  ;  x  is  opposite  the  opening  that  formerly 
led  into  the  cavity  of  the  basal  polyp.  Cf.  Fig.  29.  x  Zeiss  DD  -f  oc.  2. 

Fig.  64.  Median  vertical  section  from  a  young  medusa  intermediate  in  age  between  Figs.  31  and  32.  The  section  is 
nearly  interradial  in  position,  x  Zeiss  AA  +  oc.  2,  dt.  160. 

Figs.  65  and  66.  Tangential  sections  of  the  same  specimen,  parallel  to  the  last,  nearly  at  right  angles  to  an  interradius. 
Fig.  66  is  the  one  nearer  the  periphery,  x  Zeiss  AA  +  oc.  2,  dt.  160. 

Printed,  August,  1900. 


MEMOIRS    BOST.  soc.  NAT.  HIST.  VOL.  5.  !" 


PLATE   31. 


RPH  del. 


BIGELOW,  CASSIOPKA  XAMACHAXA. 


MEMOIRS    BOST.  Soc  NAT.  HIST.  VOL.  5. 

rkt 


PLATE   32. 


R.P.B  J,l 


23 


BIGELOW,  CASSIOPBA  XAMACIIAXA. 


MEMOIRS    BOST.  Soc.  NAT.  HIST.  VOL.  5. 


PLATE    33. 


BH;ELO\V,  CASSIOPBA   XAMACIIANA. 


MEML/;  -:.  NAT  HIST.  VOL.  5. 


Plate  34 


RPBdel 


BIGELOW,  CASSIOPEA  XAMACHANA. 


MEMOIRS    BOST.  Soc.  NAT.  HIST.  VOL.  5. 


PLATE    35. 


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BIGELOW,  CASSIOPEA  XAMACHANA. 


MEMOIRS    BOST.  Soc  NAT.  HIST.  VOL.  5. 


PLATE    36. 


52 


R.PS  del 


BKIKI.OW,  CASSIOI-KA    YAM.XCIIAXA. 


MEMOIRS    BOST.  Soc.  NAT  HIST.  VOL.  5. 


PLATE   37. 


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fl.PB.  del. 


BIGELOW,   CASSIUI-KA    XAMACIIAXA. 


MEMOIRS    BOST.  Soc  NAT.  HIST.  VOL.  5 


PLATE    38. 


BIGELOW,  CASSKU-KA    XAMACHAXA. 


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BIOLOGf 
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